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Case Study and Passage Based Questions for Class 12 Biology Chapter 5 Principles of Inheritance and Variation

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Question 1:

Study the flowchart given below and answer the questions that follow.

(i) What is a mutagen? Name a physical factor that can be mutagen. (ii) What is point mutation? Give one example. (iii) Mention two causes of frame-shift mutation.

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• Biology Important Questions
• Class 12 - Biology
• Chapter 5: Principles Inheritance Variation

Important Questions for Class 12 Chapter 5 Principles of Inheritance and Variations

Inheritance is the transfer of genes from parents to the offsprings. The principles of inheritance and variation were explained by Gregor Mendel in his experiments on a pea plant. He stated three laws of inheritance on the basis of his observations with the pea plant:

• Law of Dominance
• Law of Segregation
• Law of Independent Assortment

Very Short Answer Type Questions

Q.1. What is the cross known as when the progeny of F1 and a homozygous recessive plant is crossed? State its advantage.

A.1. The cross is a test cross. It is advantageous to determine the genotype of the parent plant.

Q.2. What are the criteria for selecting organisms to perform crosses to study the inheritance of a few traits?

A.2. The following criteria are adopted for selecting organisms:

• The traits should be easily visible.
• The organisms should have different traits.
• They should have a short life span
• They must be true breeds
• The pollination procedure should be simple.
• The traits can be manipulated easily
• Random mating of gametes should take place

A.3. The pedigree shows an autosomal recessive disorder. The parents are the carrier of the disease so the disease will be visible in only a few offsprings. The other offsprings will be either a carrier or non-carrier.

Q.4. Why did Mendel self-pollinate the tall F1 plants to get the F2 generation and crossed a pure breeding tall plant with a pure breeding dwarf plant to obtain the F1 generation?

A.4. The genotype of 50% of the offspring will resemble one parent and the rest 50% will resemble the other parent. The F1 generation obtained from the cross is heterozygous. So selfing the F1 generation is sufficient to obtain the F2 generation. It would also help to understand the inheritance of selected traits over generations.

Q.5. How are the alleles of a gene different from each other? What is its importance?

A.5. Alleles are the alternative forms of the same gene. For eg., a gene for height comprises of two alleles, one for tall (T) and the other for the dwarf (t). They differ in their nucleotide sequence due, which results in different phenotypes.

Importance :

They are essential in studying the inheritance and behaviour patterns.

They show variations in the population due to contrasting phenotypes of a character.

Q.6. How far are the genes and environment responsible for the expression of a particular trait?

A.6. The genes remain active throughout our lives, switching on and off their expression in response to the environment. The external factors such as light, temperature, nutrition, etc. are responsible for the gene expression exhibiting changes in the phenotype. Genes provide potentiality while the environment provides an opportunity for the expression of the traits.

Q.7. What is the genetic basis of the wrinkled phenotype of pea seed?

A.7. A single gene determines the shape of the seed. The (R) is for the round shape, which is dominant over (r) for the wrinkled seed. If homozygous alleles control the seed shape, it will depict the phenotype of same alleles, for eg., RR (round), rr (wrinkled). If the alleles are heterozygous, the phenotype of the dominant allele will be expressed, for eg., Rr (round).

Q.8. Why does an individual have only two alleles even if a character shows multiple alleleism?

A.8. The multiple forms of an allele that occurs on the same gene locus are known as multiple alleles. But an individual carries only two alleles. This happens because a zygote is formed by the fusion of haploid sperm and egg. They have only one allele for each trait. When the zygote becomes diploid, it has two alleles for each trait.

Q.9. How is a mutation induced by the mutagen? Explain with examples.

A.9. The mutagen changes the base sequence by insertion, deletion or substitution and induces mutation .

Q.10. Differentiate between dominance, co-dominance and incomplete dominance.

A.10.  Dominance is the phenomenon in which one variant of a gene masks the effect of a different variant of the same gene.

Co-dominance is the relationship between two alleles of a gene. In this none of the alleles are recessive and the phenotype of all the alleles are expressed.

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not expressed completely over its paired allele.

Q11.Define the chromosomal theory of inheritance?

A11. The chromosomal theory of inheritance is defined as the fundamental theory of genetics, which recognizes chromosomes as the carriers of genetic material.

Q12. Define Linkage?

A12. In genetics, the linkage is defined as the tendency of genes to remain combined together during the inheritance. This phenomenon was first observed and reported by William Bateson and R.C. Punnet in the early 1900s.

Short Answer Type Questions

Q.1. How is it possible for a child to have a blood group O if the parents have blood groups A and B?

A.1. Case I- If the father is I A and mother is I B , the child will have blood groups AB, A, B, O. Case II- If a father is I A and mother is I B , the child will have the same blood groups as in the case I, i.e., AB, A, B, and O. Thus if the parents have heterozygous alleles, the child will have blood group O.

Q.2. Explain Down’s syndrome.

A.2. Down’s syndrome is an autosomal genetic disorder caused by trisomy at chromosome 21, i.e., there is an extra copy of chromosome 21. This condition affects an individual both physically and mentally. Children born with Down’s syndrome have a flat nose and small ears. They face problem in thinking, understanding and reasoning throughout their lives. They might have trouble hearing and seeing. They are often dwarf.

Q.3. Why is it that women exceeding 40 years of age have more chances of having a child with Down’s syndrome?

A.3. The women exceeding 40 years of age have more chances of having a child with Down’s syndrome because increased age affects the meiosis of chromosomes adversely. The meiosis remains incomplete until fertilization. It remains arrested at prophase-I and the chromosome is unpaired. If the fertilization occurs after a very long gap, the chromosomes will have to remain unpaired for a longer time. The longer the time of unpairing, the greater are the chances of its non-disjunction, and hence conditions like trisomy arise.

Q.4. How was it known that the genes are located on chromosomes?

A.4. The chromosomal theory of inheritance proposed by Bovine and Sutton stated that the genes are present on specific locations on a chromosome. Later, Thomas Morgan observed mutation in the eye colour of the fruit flies and based on the inheritance patter concluded that the gene responsible for the eye colour is located on the X-chromosome.

Q.5. A plant with yellow flowers was crossed with a plant with red flowers. The F1 progeny obtained had orange flowers. What is the inheritance pattern? A.5. The inheritance is incomplete dominance . In this, a new intermediate phenotype between the two original phenotypes is obtained. One allele for a specific trait is not completely expressed over the other allele for the same trait.

Q.6. Mention the characteristics of a true-breeding line. A.6. Characteristics if true breeding is as follows:

• It undergoes self-pollination.
• It depicts stability in the inheritance for several generations.
• Provide gametes with similar traits, hence used as parents for artificial hybridization .
• Homozygous recessive plants are used to identify the genotype through a test cross.

Q.7. Who had proposed the chromosomal theory of inheritance?

A.7.  Theodor Boveri and Walter Sutton are the two scientists who were credited with developing the Chromosomal Theory of Inheritance during the early 1900s.

Q.8. What is recombination? Mention its applications with reference to genetic engineering.

A.8. Recombination is the process of producing a new combination of genes by crossing over during meiosis.

Applications:

It is a means of introducing new traits.

Variability is increased, which is necessary for natural selection.

It is used for preparing linkage chromosome maps.

The desired recombinants produced as a result of crossing over are selected by the plant breeders to produce new crop varieties.

Q.9. Why does sickle-cell anaemia persist in the human population when it is believed that the harmful alleles get eliminated from the population after a certain time?

A.9. Sickle cell anaemia is an autosomal recessive disease in which the red blood cells become sickle-shaped, inhibiting the oxygen-carrying capacity of the blood. Despite this, it protects the carrier from malaria. Individuals with heterozygotes HbAS survive more than the homozygotes HbSS because they are not exposed to the same severity of risks.

Q.10. Define artificial selection. Has it affected the process of natural selection?

A.10. Artificial selection is the intentional breeding of plants and animals where the breeders select the desired traits and make them breed to produce offsprings with the required characteristics. It is an ancient method of genetic engineering. It surely affects the process of natural selection. The individuals cannot evolve on their own. The process is a threat to biodiversity. The traits are not selected considering the fitness of the organism.

Q11.What are Sex chromosomes?

A11.  Sex chromosomes are defined as a pair of chromosomes, which determine whether an individual is male or female. In all mammals, including humans, have sex chromosomes X and Y  in their cells . Females have two X chromosomes(XX), and males have an X and a Y chromosome (XY).

Q12.What are chromosomes and who discovered chromosomes?

A12.  Chromosomes are thread-like structures present within the nucleus of a cell. Each species has a unique number of chromosomes and it varies from one organism to another. Humans have 23 pairs of chromosomes and Humans have 23 pairs of chromosomes.  

Carl Wilhelm von Nageli, a Swiss botanist, discovered chromosomes. He was the first person to observe chromosomes in plant cells in the year 1842.

Long Answer Type Questions

Q.1. What is aneuploidy? Differentiate between aneuploidy and polyploidy.

A.1. Aneuploidy is the chromosomal abnormality in which one or more chromosomes are gained or lost during meiosis due to the non-disjunction of chromosomes.

Differences between aneuploidy and polyploidy:

Polyploidy is a type of chromosomal aberration containing an entire extra set of chromosome. It may be triploid or tetraploid. This phenomenon is common in plants. It is, however, lethal in animals.

Q.2. Describe the individuals with the following chromosomal abnormalities:

• Trisomy at chromosome 21

1) Trisomy – Trisomy results in an autosomal linked genetic disorder known as Down’s syndrome. The individuals exhibit the following characteristics:

• Protruding tongue
• Slanting eyes
• Short height
• Mental retardation
• Under-developed genitals and gonads

2) XXY – The presence of an additional copy of an X-chromosome results in Kleinfelter’s syndrome . The patient exhibits the following characteristics:

• The male individual possesses feminine characteristics.
• Development of breasts in males
• Male is sterile
• Poor beard growth
• Feminine voice

3) XO – Loss of X-chromosome results in Turner’s syndrome. Characteristics:

• The female is sterile.
• The ovaries are immature.
• Webbed neck
• Thorax is shield-shaped
• Under-developed breasts.
• Puffy fingers
• Uterus is small

The standard dihybrid ratio observed is 9:3:3:1. If the two genes interact with the values will deviate. This is because when the genes are linked they do not exhibit independent assortment and remain together in the gametes and the offsprings. The dihybrid ratio thus obtained is 3:1.

Q.5. Why is Drosophila used extensively for genetic studies?

A.5. Drosophila is extensively for genetic studies because it has the following characteristics:

They have a life span of two weeks.

They can be grown in the laboratory on simple synthetic medium.

A large number of progenies are produced by a single mating.

The male and the female Drosophila can be differentiated easily.

It has many variations easily visible under a simple microscope.

Q6.List out the characteristics of the chromosome theory of Inheritance.

The important characteristics of the chromosome theory of Inheritance are:

• Fertilization restores diploid condition.
• Chromosomes segregate and assort independently.
• Homologous chromosomes separate at the time of meiosis.
• Both chromosomes, as well as genes, exist in pairs within the diploid cells.
• Gamete contains only one chromosome of a particular type and only one of the two alleles of a character.

Q7.Define autosome, hemizygous, homozygous, and heterozygous?

Autosome– All chromosomes apart from the sex chromosomes are called the Autosomes. The number of autosomes differs from one organism to another. Humans have 44 number or 22 pairs of autosomes .

Hemizygous– It is a condition in which an organism has only one copy of a gene or DNA sequence present in diploid cells.

Homozygous — It is a condition in which an organism has two similar alleles of a given gene (XX).

Heterozygous –It is a condition in which an organism has two different alleles of a given gene (XY) .

Q8.What are Sex-linkage?

A8. Sex linkage can be defined as the phenotypic expression of an allele, which is dependent on the individual’s gender. It describes the presentation of the chromosome and the sex-specific patterns of inheritance . Sex linkage is directly tied to the sex chromosomes – homogametic sex and heterogametic sex. In mammals, the homogametic sex  (XX) is female and the heterogametic sex (XY) is male. Thus the sex-linked genes are carried on the X chromosome.

Q9. Why is colour blindness more prominent in males than females?

A9. Colour blindness is a sex-linked disorder and the genes responsible are present on the X-chromosome. To become affected by the disease, the female should possess the alleles for colour blindness on both the X-chromosomes. If the allele is present on only one chromosome, the female becomes a carrier of the disease. Since males have only one X-chromosome, it carrying the allele renders them affected. That is why males are more prone to colour blindness .

Q10. Why did scientists select fruit flies for his genetics experiments?

A10.  Drosophila melanogaster is a small common fly species, which belongs to the family Drosophilidae. This species is generally known as the vinegar fly or a fruit fly.  

In the year 1830, Drosophila melanogaster was established as a key model organism for biomedical science and it is due to the considerable biological similarity to mammals and an abundance of available genetic tools.

Like humans, these fruit flies species have a similar distribution of chromosomes. An individual with a pair of X chromosomes is female fruit fly and an individual with one X and one Y chromosome is male.

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Class 12th Biology - Principles of Inheritance and Variation Case Study Questions and Answers 2022 - 2023

Class 12th Biology - Principles of Inheritance and Variation Case Study Questions and Answers 2022 - 2023 Study Materials Sep-08 , 2022

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Principles of inheritance and variation case study questions with answer key.

Final Semester - June 2015

Two independent monohybrid crosses were carried out involving a tall pea plant with a dwarf pea plant. In the first cross, the offspring population had equal number of tall and dwarf plants, whereas in the second cross, it was different. Work out the crosses and explain giving reasons for the difference in the offspring populations.

ABO blood group character in human population exhibits four possible phenotypes and six different genotypes. Explain the different mechanisms of inheritance involved in exhibiting the possibility of four phenotypes and six genotypes.

In pea plants, let symbol Y represent dominant yellow, symbol y, the recessive green, symbol R, the round seed shape, and symbol r, the wrinkled seed shape. A typical Mendelian dihybrid cross was carried out starting with homozygous dominant and recessive parents. Answer the following questions. (a) Write the genotype and phenotype of the F 1 offspring. (b) The genetic make up of the gametes produced by F 1   individual. (c) Give the phenotypic ratio of F 2 generation.

During a cytological study conducted on the chromosomes of certain insect species, it was observed that only 50% of the sperms had a specific structure after spermatogenesis. (a) Name the scientist who conducted the above experiment. (b) Name the structure, the scientist observed. (c) Give an example of an insect that could possibly show such a phenomenon and name the mechanism of sex determination. (d) Write the sex chromosome complement of males and females.

Read the following and answer any four questions from (i) to (v) given below: Prashant wanted to find the genotype of a pea plant bearing purple coloured flowers in his kitchen garden. For this, he crossed purple flowered plant with white flowered plant. As a result, all plants which were produced had purple flower only. Upon selfing these plants, 75 purple flower plants and 25 white flower plants were produced. Now, he can determine the genotype of a purple flowered plant by crossing it with a white flowered plant. (i) Which of the following cannot be derived from the crosses done by Prashant?

(ii) To determine the genotype of a purple flowered plant, Prashant crossed this plant with a white flowered plant. This cross represents a

(iii) In white flowered plant, allele is expressed in

generation

(iv) The character, i.e., purple colour of the flowers that appeared in the first filial generation is called

(v) Assertion : A geneticist crossed two plants and he obtained 50% purple flowered plants and 50% white flowered plants. Reasons : Purple coloured flower plant might be heterozygous.

(ii) Teacher asked to conduct an experiment on Drosophila because

(iii) Genes white eyed and yellow bodied located very close to one another on the same chromosome tend to be transmitted together are called

(iv) Select the correct statement regarding the given experiment.

(v) Assertion : When yellow bodied, white eyed Drosophila females were hybridised with brown-bodied, red eyed males; and FI progeny was intercross ed, F 2 ratio deviated from 9: 3: 3: 1. Reason : When two genes in a dihybrid are on the same chromosome, the proportion of parental gene combinations are much higher than the non-parental type.

Read the following and answer any four questions from (i) to (v) given below : Turner's syndrome is an example of mono somy. It is formed by the union of an allosome free egg and a normal 'X' containing sperm or a normal egg and an allosome free sperm. The individual has 2n = 45 chromosomes (44 + X0) instead of 46. Such individuals are sterile females who have rudimentary ovaries, under developed breasts, small uterus, short stature, webbed neck and abnormal intelligence. They may not menstruate or ovulate. This disorder can be treated by giving female sex hormone to the women from the age of puberty to make them develop breasts and have menstruation. This makes them feel more normal. (i) Number of Barr body present in a female with Turner's syndrome is

(ii) Turner's syndrome is an example of

(iii) Turner's syndrome is a/an

(iv) Which of the following statements regarding Turner's syndrome is incorrect?

(v) Assertion : Turner's syndrome is caused due to absence of anyone of the X and Y sex chromosome. Reason : Individuals suffering from Turner's syndrome show masculine as well as feminine development

Read the following and answer any four questions from (i) to (v) given below : According to Mendel, one gene control the expression of one character only. The ability of a gene to have multiple phenotypic effect because it influences a number of characters is an exception. The gene having a multiple phenotypic effect because of its ability to control of two or more characters can be seen in cotton. In cotton, a gene for the lint also influences the height of plant, size of the ball, number of ovules and viability of seeds. (i) Genes with multiple phenotypic effects are known as

(ii) Which of the following disorder is an example of genes with multiple phenotypic effects?

(iii) Which of the following is an example of gene with multiple phenotypic effect?

(iv) Which of the following statements is not correct regarding genes with multiple phenotypic effect?

(v) Assertion : In garden pea, the gene which controls the flower colour also controls the colour of the seed coat and presence of red spots in the leafaxils. Reason : A pleiotropic gene influences more than one trait.

Read the following and answer any four questions from (i) to (v) given below: Haemophilia is a sex linked disease which is also known as bleeder's disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of anti-haemophilic globulin or factor VIII and plasma thromboplastin factor IX essential for it. As a result of continuous bleeding the patient may die of blood loss. Colour blindness is another type of sex linked trait in which the eye fails to distinguish red and green colours. Vision is however, not affected and the colour blind can, lead a normal life, reading, writing and driving (distinguishing traffic lights by their position).(i) If a haemophilic man marries a woman whose father was haemophilic and mother was normal then which of the following holds true for their progenies?

(ii) A man whose father was colourblind and mother was normal marries a woman whose father was haemophilic and mother was normal. Which of the following is true for their progenies? [Note: Percentage is from the total number of progenies.

(iii) Which of the following statements is incorrect regarding haemophilia?

(iv) Anup is having colourblindness and is married to Soni who is normal. What is the chance that their son will have the disease?

(ii) Due to mutation Y the shape of RBCs under oxygen tension will be

(iii) GUG is code for

(iv) Which of the following genotype shows diseased phenotype due to mutation Y?

Hb

Hb

Hb

	and 3 child in F
(a) Hb Hb , Hb Hb	Hb Hb , Hb Hb
(b) Hb Hb , Hb Hb	Hb Hb , Hb Hb
(c) Hb HbA, Hb Hb	Hb Hb , HbS Hb
(d) Hb Hbs, Hb Hbs	Hb Hb , Hb Hb

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Principles of Inheritance and Variation Class 12 Important Questions and Answers Biology Chapter 5

July 30, 2022 by Bhagya

We have given these  Class 12 Biology Important Questions Chapter 5 Principles of Inheritance and Variation to solve different types of questions in the exam. Go through these Class 12 Biology Chapter 5 Important Questions, Principles of Inheritance and Variation Important Questions & Previous Year Questions to score good marks in the board examination.

Class 12 Biology Chapter 5 Important Questions Principles of Inheritance and Variation

Question 1. Name the pattern of inheritance where F 1 phenotype (i) resembles only one of the two parents. (ii) does not resemble either of the two parents and is in between the two. (All India 2019) Or Name the respective pattern of inheritance, where F 1 phenotype (i) does not resemble either of the two parents and is in between the two. (ii) resembles only one of the two parents. (All India 2012) Answer: (i) Dominance (ii) Incomplete dominance Or (i) Incomplete dominance (ii) Dominance.

Question 2. British geneticist RC Punnett developed a graphical representation of a genetic cross called ‘Punnett Square’. Mention the possible result this representation predicts of the genetic cross carried. (Delhi 2019) Answer: Punnett square helps to predict the probability of all the possible genotypes of offspring in a genetic cross.

Question 3. Name the type of cross that would help to find the genotype of a pea plant bearing violet flowers. (All India 2017) Answer: To find the genotype of a pea plant bearing violet flowers, test cross would be carried out in which the plant with dominant trait, i.e. violet flowers, will be crossed with its recessive parent.

Question 4. State a difference between a gene and an allele. (All India 2016) Answer: A unit of inheritance which is passed down from parent to offspring through the gametes over successive generations is known as gene. Genes consist of a pair of contrasting forms for a character that are known as alleles.

Question 5. Give an example of polygenic trait in humans. (Delhi 2016C) Or On what basis is the skin colour in humans considered polygenic? (Delhi 2016) Answer: An example of a polygenic trait in humans is skin colour. Or Skin colour is considered to be a polygenic trait because it is under the control of many genes.

Question 6. A geneticist interested in studying variations and patterns of inheritance in living beings prefers to choose organisms for experiments with shorter life cycle. Provide a reason. (Delhi 2015) Answer: A geneticist interested in studying variations and patterns of inheritance in living beings prefers to choose organisms with shorter life cycle, because it enables the geneticist to study many generations of the organism in a short time period.

Question 7. Mention any two contrasting traits with respect to seeds in pea plant that were studied by Mendel. (All India 2014) Answer: Two contrasting seed traits studied by Mendel are

• Seed shape Round and wrinkled.
• Seed colour Yellow and green.

Question 8. What are ‘true-breeding lines’ that are used to study inheritance pattern of traits in plants. (Delhi 2014) Answer: True-breeding lines are those plants, which have undergone continuous self-pollination and show stable trait inheritance and expression for several generations.

Question 9. How many kinds of phenotype would you expect in F 2 -generation in a monohybrid cross exhibiting codominance? (All India 2014) Answer: In codominance, alleles are able to express themselves independently when present together. Thus, in a monohybrid cross there would be three kinds of phenotype in the F 2 -generation showing codominance.

Question 10. Name the stage of cell division where segregation of an independent pair of chromosomes occurs. (All India 2014) Or Name the event during cell division cycle that results in the gain and loss of chromosomes. (Delhi 2011) Answer: During meiotic anaphase-I of cell division, the separation of independent pair of chromosomes occurs. Or Non-disjunction of chromosomes during anaphase-I of meiosis results in the gain or loss of chromosomes.

Question 11. A garden pea plant (A) produced inflated yellow pod and another plant (B) of the same species produced constricted green pods. Identify the dominant traits. (Delhi 2012) Answer: The dominant trait in the pea plant is inflated green pods while the recessive trait is constricted yellow pod?

Question 12. A garden pea plant produced axial white flowers another of the same species produced terminal violet flowers. Identify the dominant traits. (All India 2012) Answer: The dominant trait in the pea plant is axial violet flowers, while the recessive trait is terminal white flowers.

Question 13. In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental types, as experimentally shown by Morgan and his group? (All India 2012) Answer: The proportion of parental gene combination is much higher than non-parental types, when the two genes show linkage and are inherited together.

Question 14. Write possible genotypes Mendel got when he crossed F 1 tall plant with a dwarf pea plant. (Foreign 2012) Answer: Tt and tt (in ratio of 1:1) genotypes were obtained on crossing F 1 tall plant with a dwarf parent plant. It is a test cross.

Question 15. Garden pea plant produced round, green seed. Another of same species produced wrinkled yellow seeds. Identify dominant traits. (Foreign 2012) Answer: The dominant trait in pea plant is round and green seeds, while the recessive trait is wrinkled and yellow seeds.

Question 16. Mention two contrasting flower related traits studied by Mendel in pea plant experiments. (All India 2011C) Answer: The two contrasting flower traits in pea plant are

• Violet flowers and white flowers.
• Axial flowers and terminal flowers.

Question 17. Name the contrasting pod related traits studied by Mendel in his pea plant experiment. (All India 2011C) Answer: The two contrasting pod related traits in pea plant are

• Inflated/Constricted shape.
• Green/Yellow colour.

Question 18. Mention the type of allele that expresses itself only in homozygous state in an organism. (Foreign 2011) Answer: Recessive allele expresses itself only in homozygous condition because in the presence of a dominant allele its effect is masked.

Question 19. Pea flowers produce assured seed sets. Give a reason. (All India 2010) Answer: Pea flowers produce assured seed sets because they have cleistogamous flowers, which undergo natural self-pollination.

Question 20. Explain polygenic inheritance with the help of an example. (All India 2019) Answer: Refer to text ‘Polygenic Inheritance, on page no. 94 and 95.

Question 21. When does a geneticist need to carry a test cross? (Foreign 2015) Or How would you find the genotype of an organism exhibiting a dominant phenotype? (Delhi 2012C) Answer: A geneticist needs to carry a test cross when he/she wants to determine the genotype of an organism, with a dominant phenotype trait, whether it is homozygous or heterozygous. Or Genotype of the dominant phenotype is determined by a test cross. In it, the F 1 progeny is crossed to its recessive parent. When F 1 progeny (heterozygous) crossed with dwarf plant, the monohybrid test cross ratio is 1 : 1. But, all tall plants are obtained when both homozygous parents are crossed.

Question 22. Why did TH Morgan select Drosophila melanogaster to study sex-linked genes for his lab experiments. (Foreign 2015) Or Write the scientific name of the fruitfly. Why did Morgan prefer to work with fruit flies for his experiments? State any three reasons. (All India 2014) Answer: The scientific name of fruitfly is Drosophila melanogaster. TH Morgan preferred this organism for his study because of the following reasons

• It has fast and short life cycle.
• It has’only four pairs of chromosomes.
• It reproduces quickly.

Question 23. Give an example of a gene responsible for multiple phenotypic expressions. What are such genes called? State the cause that is responsible for such an effect. (Foreign 2015) Or Explain pleiotropy with the help of an example. (Foreign 2014) Answer: Pleiotropy is the phenomenon in which a single gene exhibits multiple phenotypic expressions. The genes exhibiting pleiotropy are called pleiotrppic genes. Pleiotropism occurs mainly because of mutation in a particular gene, e.g. phenylketonuria which is a disorder caused by mutation in the gene coding for the enzyme phenylalanine hydroxylase. In the absence of this enzyme, phenylalanine is not converted into tyrosine and accumulation of phenylalanine takes place. The affected individual shows hair and skin pigmentation and mental problems.

Question 24. The F 2 progeny of a monohybrid cross showed phenotypic and genotypic ratio as 1 : 2 : 1, unlike that of Mendel’s monohybrid F 2 ratio. With the help of a suitable example, work out a cross and explain how it is possible. (All India 2015) Or Why are F 2 phenotypic and genotypic ratios are same in a cross between red flowered snapdragon and white flowered snapdragon plants? Explain with the help of cross. Delhi 2010 Answer: The given condition represents the case of incomplete dominance. In snapdragon, the inheritance of flower colour shows incomplete dominance. Neither of the alleles of gene for flower colour is completely dominant over the other and hybrid shows an intermediate phenotype. Therefore, F 2 phenotypic and genotypic ratios are same in a cross between red flowered snapdragon and white flowered snapdragon plants.

Question 25. With the help of one example, explain the phenomena of codominance and multiple allelism in human population. (All India 2014) Answer: In human population, the phenomena of codominance and multiple allelism can be explained by the inheritance pattern of ABO blood groups which are controlled by three alleles, i.e. I A ,I B and I.

• Codominance I A and I B both are codominant as both of them express themselves independently in blood group AB (I A I B ). There is no mixing of the effects of two alleles and the expressed phenotype is the combination of two phenotypes. They do not follow Mendelian inheritance.
• Multiple allelism In this phenomenon, genes exist in more than two allelic forms or combinations. For example, the gene for blood group exists in three allelic forms I A , I B and i. These alleles are produced due to repeated mutation of the same gene in different direction. They do not follow Mendelian pattern of inheritance.

Question 26. Linkage and crossing over of genes are alternatives of each other. Justify with the help of an example. (All India 2014) Answer: Linkage is the tendency of certain loci or alleles (genes) to be inherited together. While crossing over in the segregation of genes. The former helps to preserve parental characters in offsprings whearas the latter produces new combination of characters. The genes on a chromosome either follow linkage path or crossing over to form the gametes during gametogenesis in human. Therefore, linkage and crossing over of genes are alternatives of each other.

Question 27. In snapdragon, a cross between true-breeding red flowered (RR) plants and true-breeding white flowered (rr) plants showed a progeny of plants with all pink flowers. (i) The appearance of pink flowers is not known as blending. Why? (ii) What is this phenomenon known as? (All India 2014) Answer: (i) Blending is the mixing of two colours, but in this example red and white colours appear independently at cellular level. Thus, no blending occurs. The red and white colours reappear in F 2 -generation. (ii) This phenomenon is known as incomplete dominance.

Question 29. How does the gene T control ABO blood group in humans? Write the effect the gene has on the structure of red blood cells. (Delhi 2014) Answer: In humans, the ABO blood groups are controlled by a gene called gene ‘I’. It has three alleles, i.e. I A , I B and i. A person possesses any two of the three alleles. I A and I B are codominant and they both are dominant over i. These alleles help to determine the blood group of a person. The plasma membrane of red blood cells has sugar polymers that protrude out from its surface and the kind of sugar is regulated by the gene ‘I’ of ABO blood group. The alleles I A and I B produce enzymes that produce A and B types of sugar respectively on the surface of red blood cells, while allele i does not produce any sugar.

Question 31. A cross between a red flower bearing plant and a white flower bearing plant of Antirrhinum produced all plants having pink flowers. Work out a cross to explain how this is possible. (All India 2013) Or Explain the mechanism of inheritance of the progeny produced when two Antirrhinum pink flowers were crossed. (All India 2012) Answer: Cross of red flowered Antirrhinum with white flowered plant produces pink flowered plants. This shows incomplete dominance. For cross, Refer to Answer No. 24.

Question 32. Work out a cross to find the genotype of a tall pea plant. Name the type of cross. (All India 2013) Answer: To know the genotype of tall pea plant, test cross is to be performed. It is the cross between F 1 -hybrid and its recessive parent. For cross, Refer to Answer No. 28 (i).

Question 33. Differentiate between multiple allelism and pleiotropy with the help of an example of each. (Delhi 2013c) Answer: Differences between multiple allelism and pleiotropy are Multiple allelism This occurs when one trait is controlled by more than two alleles. e.g. ABO blood grouping.

Pleiotropy This occurs when one gene controls many traits. e.g. Phenylketonuria (PKU).

Question 36. How is the phenotypic ratio of F 2 -generation in a dihybrid cross is different from monohybrid cross? (All India 2012) Answer: In a monohybrid cross, the phenotypic ratio of F 2 -generation is 3 : 1, whereas in dihybrid cross, the pheonotypic ratio of F 2 -generation is 9 : 3 : 3 : 1.

Question 37. In a dihybrid cross, white-eyed, yellow-bodied female Drosophila crossed with red-eyed, brown-bodied male Drosophila produced in F 2 -generation 1.3% recombinants and 98.7% progeny with parental type combinations. This observation of Morgan deviated from Mendelian F 2 -phenotypic dihybrid ratio. Explain, giving reasons Morgan’s observation. (Foreign 2011) Answer: The results obtained were due to the linkage. It is the phenomenon in which two or more linked genes are inherited together and their frequency of recombination in a test cross progeny is less than the expected 50%. In Morgan’s experiment on Drosophila, the genes for eye colour and body colour show linkage and do not allow crossing over during gamete formation. Hence, parental type progeny is in greater ratio than that of recombinants.

Question 38. Explain the phenomena of dominance, multiple allelism and codominance taking human ABO blood group as an example. (All India 2019) Answer: Refer to text on page no. 93 and 94.

Question 39. Compare in any three ways the chromosomal theory of inheritance as proposed by Sutton and Bovery with that of experimental results on pea plant presented by Mendel. (Delhi 2019) Answer: Through any of the given ways chromosomal theory of inheritance and experimental results presented by Mendel can be compared

• In a diploid organism, the factors (genes) and chromosomes occur in pairs.
• Both chromosomes as well as genes segregate at the time of gamete formation such that only one of each pair is transmitted to a gamete.
• A gamete contains only one chromosome of a type and only one of the two alleles of a trait.
• The paired condition of both chromosomes as well as Mendelian factors is restored during fertilisation. (Any three)

Question 40. (i) Explain linkage and recombination as put forth by TH Morgan based on his observations with Drosophila melanogaster crossing experiment. (ii) Write the basis on which Alfred Sturtevant explained gene mapping. (Delhi 2019) Answer: (i) TH Morgan studied X-linked gene in Drosophila and saw that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. He attributed this due to the physical association or linkage of the two genes on a chromosome and coined the term linkage. The term recombination describes the generation of non-parental gene combination in offsprings.

(ii) Alfred Sturtevant explained gene mapping by using the frequency of recombination between the gene pairs on the same chromosome as a measure of the distance between genes and he mapped their position on the chromosome.

Question 43. Although Mendel published his work on inheritance of characters in 1865 but for several reasons, it remained unrecognised till 1900. Explain giving three reasons, why did it take so long. (Delhi 2016C) Or Mendel published his work on inheritance of characters in 1865, but it remained unrecognised till 1900. Give three reasons for the delay in accepting his work. (Delhi 2014) Answer: The following are the three reasons that led to delay in accepting Mendel’s work.

• Lack of communication and less published work.
• His concept of factors (genes) as discrete units which did not blend with each other was not accepted in the light of variations occurring continuously in nature.
• Mendel’s approach to explain biological phenomenon with the help of mathematics was also not accepted.

Question 44. Explain the laws that Mendel derived from his monohybrid crosses. (Delhi 2016C) Answer: From mbnohybrid crosses, Mendel derived law of dominance and law of segregation. Refer to text on page no. 92 for detailed description of these laws.

Question 47. Explain with the help of a suitable example, the inheritance of a trait where two different dominant alleles of a trait express themselves simultaneously in the progeny. Name this kind of inheritance pattern. (All India 2014C) Answer: Codominance is the inheritance of a trait where two different dominant alleles of a trait express themselves simultaneously in the progeny. For example, ABO blood groups in human population.

• Gene T for blood group exhibits three allelic forms, i.e. I A , I B and i.
• I A and I B produce RBC surface antigen A and B respectively, whereas i does not produce any antigen.
• I A and I B are codominant alleles, and they both are dominant over ‘i’ which is a recessive allele.
• In case I A and I B are present together, both express themselves equally and produce both surface antigen A and B. The resultant offspring is of ‘AB’ blood type.

Allele from parent 1	Allele from parent 2	Genotypes of offsprings	Blood types of offsprings
I	I	I I	A
I	I	I I	AB
I	i	I i	A
I	I	I I	AB
I	I	I I	B
I	i	I i	B
i	i	ii	O

Question 48. Explain polygenic inheritance with the help of a suitable example. (All India 2014) Answer: Polygenic inheritance is an inheritance pattern controlled by three or more genes (multiple genes) and the graded phenotypes are due to the additive or cumulative effect of all the different genes of the trait, e.g. skin colour in human population shows variation.

Skin colour in humans is produced by a pigment called melanin. The quantity of melanin is due to three pairs of polygenes (A, B and C). If a black or very dark (AA BB CC) and white or very light (aa bb cc) individuals marry each other, the offsprings or individuals of F 1 -generation show intermediate colour and they are often called mulatto (Aa Bb Cc).

A total of eight allele combinations are possible in the gametes forming 27 distinct genotypes distributed into 7 phenotypes, i.e. 1 very dark, 6 dark, 15 fairly dark, 20 intermediate, 15 fairly light and 1 very light.

Question 49. Morgan carried out several dihybrid crosses in Drosophila and found F 2 ratios deviated very significantly from the expected Mendelian ratio. Explain his finding with the help of an example. (All India 2014C; Delhi 2010) Answer: Morgan’s studies on Drosophila were based on the genes that were located on the X-chromosome. He found when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. Morgan stated this association as linkage to describe the physical association of genes on a chromosome. Recombination is a term used to describe the generation of non-parental gene combination. Morgan also found that some genes were tightly linked (low recombination) and others were loosely linked (high recombination). He concluded that in case of inheritance of linked genes, the phenotypic ratio deviates from expected 9 : 3 : 3 : 1 ratio of Mendel’s dihybrid cross.

To prove his findings, Morgan hybridised yellow-bodied and white-eyed females with brown-bodied and red-eyed males (wild type) and intercrossed their F 1 -progeny (cross A). It was observed that the two genes did not segregate independently for each other and the F 2 -ratio deviated significantly from 9 : 3 : 3 : 1 ratio.

In F 2 -generation, parental combinations were 98.7% and the recombinants were 1.3%. In another cross (cross B), between white-bodied female fly with miniature wing and a male fly with yellow body and normal wing, parental combinations were 62.8% and recombinants were 37.2% in F 2 -generation. Thus, it was proved from the crosses that the linkage between genes for yellow body and white eyes was stronger than the linkage between the white body and miniature wing.

Question 50. (i) Write the conclusion Mendel arrived at on dominance of traits on the basis of monohybrid crosses that he carried out in pea plants. (ii) Explain why a recessive allele is unable to express itself in a heterozygous state. (Foreign 2014) Answer: (i) In a monohybrid cross in pea plant, Mendel found that only dominant trait expresses itself in offspring no matter it is whether present in homozygous state (TT) or in heterozygous state (Tt). Dominant trait does not require another similar allele to produce its effect on the phenotype, in fact it has the ability to mask the effect of recessive allele. Based on this observation, Mendel proposed the law of dominance.

(ii) Since, the characters are controlled by genes which occur in pair, when two alternate forms of a trait or character (genes or alleles) are present in an organism, only one factor expresses itself in F 1 -generation. This factor is dominant, while the other factor that remains masked by the dominant factor is called as recessive.

The recessive allele is unable to express itself in a heterozygous state because it forms an incomplete or defective polypeptide or enzyme, so its expression does not contain any effect. In contrast, dominant allele can form complete polypeptide or enzyme to express its effect.

Question 51. In pea plants, the colour of the flower is either violet or white, whereas human skin colour shows many gradation. Explain giving reasons how it is possible. (Delhi 2013C) Answer: In pea plants, the colour of the flower is either violet or white because the colour is purely dependent on two alleles and the crossing between them, i.e. violet and white in the parents generation, which results in F 1 -generation. Thus, the resultant offsprings are either violet or white coloured. Hence, the inheritance pattern of flower colour in pea plant follows the law of dominance.

But in case of humans, skin colour is produced by polygenes. Such inheritance is controlled by one or more genes in which dominant alleles have cumulative effect with each dominant allele expressing a part of the trait. The full trait is shown only when all the dominant alleles are present together.

The quantity of human skin pigment melanin determines the human skin colour (i.e. very dark, dark, fairly dark, intermediate, fairly light, light and very light). Refer to Answer No. 48.

Question 52. (i) Explain the phenomena of multiple allelism and codominance taking ABO blood group as an example. (All India 2012) (ii) What is the phenotype of the following? (a) I A i (b) ii Answer: (i) Refer to Answer No. 25. (ii) Phenotypes of given blood genotypes are as follows (a) I A i – ‘A’ blood group (b) ii – ‘O’blood group

Purple flowered plants : White flowered plants are in the ratio of 482 : 162 which is approximately equal to 3 : 1.

The genetic mechanism for these results is explained below: (i) Factors segregate from each other during gamete formation that remain together in a parent. (ii) A homozygous parent produces all gametes that are similar, while heterozyogous parent produces two kinds of gametes in equal ratio.

Question 54. Work out a cross between true breeding red and white flowered dog flower plants (snapdragon) upto F 2 progeny. Explain the results of F 1 and F 2 -generation. (Foreign 2010) Answer: For cross, Refer to Answer No. 24. In F 1 -generation Pink flowered plants obtained. It is due to incomplete dominance. In F 2 -generation Alleles of the hybrid (F 1 ) segregate during gamete formation and the parental characters reappear without any change. So, the phenotypic and genotypic ratios in F 2 -generation are same.

Question 55. (i) Work out the crosses so as to obtain the phenotypic ratios given below: (a) 1 : 2 : 1 (in F 2 -generation) (b) 3 : 1 (in F 2 -generation) (c) 1 : 1 (in F 1 -generation) (ii) Differentiate between pleiotropy and polygenic inheritance patterns. (All India 2019) Answer: (i) (a) 1 : 2 : 1 (in F 2 -generation ) is the phenotypic ratio of incomplete dominance. Refer to figure 5.3 on page no. 93.

(b) 3 : 1 (in F 2 -generation) is the phenotypic ratio of monohybrid cross. Refer to figure 5.1 on page no. 91.

(c) 1 : 1 (in F 1/sub>-generation) is the phenotypic ratio of test cross. Refer to text and figure of ‘Test cross’ on page no. 91 and 92.

(ii) Differences between pleiotropy and polygenic inheritance are as follows

Pleiotropy	Polygenic inheritance
Single gene product confers many physiological effects.	Single phenotypic effect is under the control of many genes.
The genes involved are called pleiotropic genes.	The genes involved are called polygenes.
e.g. phenylketonuria.	e.g. human skin colour.

Question 56. Differentiate between incomplete dominance and codominance. Substantiate your answer with one example of each. (Delhi 2019) Answer: Differences between codominance and incomplete dominance are as follows

Codominance	Incomplete dominance
It is the appearance of both parental phenotypes together in the offspring when a cross is done between individuals with two different phenotypes.	It is the appearance of an intermediate phenotype, which is a combination of both parental alleles when a cross is done between individuals with two different phenotypes.
Both parental alleles produce their effect independently.	Effect of the two parental alleles is intermediate on the offspring.
Both parental alleles can be observed in the offspring.	None of parental alleles can be observed in the offspring.
Examples include ABO blood group, etc. Six different genotypes of human ABO blood group show four phenotypes-A, B, AB and O.	Examples include inheritance of flower colour in the dogflower, etc. Here, the genotypic ratio of F remains same as Mendel’s monohybrid cross, i.e. 1 : 2 : 1, but phenotypic ratio changes from 3 : 1 to 1 : 2 : 1.

Question 57. (i) Write the scientific name of the organism Thomas Hunt Morgan and his colleagues worked with for their experiments. Explain the correlation between linkage and recombination with respect to genes as studied by them. (ii) How did Sturtevant explain gene mapping while working with Morgan? (2018) Answer: (i) Thomas Hunt Morgan and his colleagues worked on Drosophila melanogaster. Relation between Linkage and Recombination: Morgan carried out dihybrid crosses in Drosophila to study sex-linked genes. Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males. He intercrossed their F 1 – progeny. It was observed that the two genes did not segregate independently of each other. The F 2 ratio deviated from the ratio of 9 : 3 : 3 : 1.

It was known to Morgan and his colleagues that genes were located on X-chromosomes. They noticed that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental combination was very high in comparison to non-parental type. He attributed this due to the physical association or linkage of the two genes. To describe this physical association of gene, he coined the term linkage. Recombination term was used to describe the generation of non-parental gene combinations. In his experiments, he observed that even when genes were grouped on the same chromosome, some genes were very tightly linked and showed very low recombination. On the other hand, loosely linked genes showed higher recombination.

(ii) Sturtevant, a student of Morgan, used the frequency of recombination between the gene pairs on the same chromosomes as a measure of the distance between genes. He mapped the position of genes on the chromosome by using this information.

These factors randomly rearrange in the offspring producing both parental and new combination of characters. It means inheritance of one character does not affect the inheritance of another character and both characters assort independently during gamete formation. The Punnett square can be used to understand the independent segregation of the two pairs of genes during meiosis.

A total of eight allele combinations are possible in the gametes forming 27 distinct genotypes distributed into 7 phenotypes, i.e. 1 very dark, 6 dark, 15 fairly dark, 20 intermediate, 15 fairly light, 6 light and 1 very light.

(ii) In pleiotropy, single gene product may produce multiple or more than one phenotypic effect whereas in polygenic inheritance single phenotypic trait (human skin colour) is controlled by 3 pairs of genes (A, B and C). In Mendelian inheritance, one gene controls one phenotypic character (flower colour red or white). However, in polygenic inheritnace one phenotype is controlled by more than one gene.

(ii) ABO blood grouping in humans shows the phenomenon of codominance. Refer to Answer No. 29 and 47.

Differences between law of segregation and law of independent assortment are:

Law of segregation	Law of independent assortment
It is based on the monohybrid cross.	It is based on the dihybrid cross.
It explains non-mixing of two alleles of a gene at the time of gamete formation.	It explains non-mixing of characters during their inheritance to the next generation.

The ratio 9 : 3 : 3 : 1 was. obtained because the factors of height of plant and those for shape of seeds have segregated independently and each gamete has one factor for each of these two traits.

(iii) This cross is known as dihybrid test cross. The purpose of this cross is to determine the relationship between different allelic pairs.

Question 64. Work out a monohybrid cross up to F 1 -generation between two pea plants and two Antirrhinum plants both having contrasting traits with respect to colour of flower. Comment on the pattern of inheritance in the crosses carried above. (All India 2014C) Answer: Refer to Answer No. 53 for cross showing inheritance pattern of flower colour in garden pea plant. Phenotypic ratio Purple : White 3 : 1 Genotypic ratio PP : Pp : pp 1 : 2 : 1 Inheritance of flower colour in garden pea shows true dominance. In F 1 -generation, dominant colour purple is expressed and in F 2 -generation, both dominant (purple) and recessive (white) colours are expressed in the ratio of 3 : 1.

Inheritance pattern of flower colour in Antirrhium (snapdragon), Refer to Answer No. 24. Inheritance in snapdragon flower colour shows incomplete dominance. In this phenomenon, neither of the two alleles is completely dominant over the other and the hybrid is intermediate between the two. Hence, red is homozygous dominant, white is homozygous recessive, while hybrid is intermediate, i.e. pink.

Question 65. (i) Differentiate between dominance and co-dominance. (ii) Explain codominance taking an example of human blood groups in the population. (All India 2013) Answer: (i) Difference between dominance and codominance is as follows Dominance: Out of the two contrasting alleles of a gene, only one can produce effect in heterozygous condition, e.g. trait of tallness in pea plants.

Codominance: Both the alternative forms of a gene can produce effect in heterozygous condition, e.g. ABO blood grouping in humans.

(ii) Refer to Answer No. 47.

Question 66. (i) Explain Mendel’s law of independent assortment by taking a suitable example. (ii) How did Morgan show the deviation in inheritance pattern in Drosophila with respect to this law? (All India 2013) Answer: (i) Refer to Answer No. 58. (ii) Morgan found that linkage is an exception to the law of independent assortment. Conclusion of Morgan’s studies, Refer to Answer No. 49.

Question 67. What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum. Work out the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance? (Delhi 2013) Or Pea seeds with BB alleles have round seeds and large starch grains, while seeds with bb alleles have wrinkled seeds with small starch grains. Work out the cross between these two parents. Explain the phenotypic ratio of the progeny with respect to seed shape and the starch grain size of the progeny produced. (All India 2012C) Answer: The starch synthesis in pea plants is controlled by a single gene. It has two alleles B and b. BB homozygotes produce large starch grains as compared to that produced by bb homozygotes.

Deviation from Mendel’s law of dominance: If starch grain size is considered as the phenotype, then, the alleles show incomplete dominance. Thus, dominance is not an autonomous feature of a gene, it depends on gene product and production of particular phenotype from this product.

Question 68. Differentiate between the following. (i) Polygenic inheritance and pleiotropy. (ii) Dominance, codominance and incomplete dominance. (All India 2013C; Delhi 2011) Answer: (i) Differences between polygenic inheritance and. pleiotropy are as follows

Polygenic inheritance	Pleiotropy
Single phenotypic effect is under the control of many genes.	Single gene product confers many phenotypic effects.
The genes involved are called polygenes, e.g. human skin colour.	The genes involved are called pleiotropic genes. eg-phenylketonuria.

(ii) Differences between dominance, codominance and incomplete dominance are as follows

Dominance	Codominance	Incomplete dominance
It is a relationship between alleles of a single gene, in which one allele masks the phenotypic expression of another allele at the same gene locus, e.g. tallness in pea plant.	It is the phenomenon of expression of both the alleles in heterozygous condition. In this, alleles do not show dominant-recessive relationship and are able to express themselves independently, e.g. ABO blood group in humans.	It is also known as partial or mosaic dominance where none of the two contrasting alleles or factors is dominant, e.g. incomplete dominance in 4 ‘O’ clock plant.

Incomplete dominance It is also known as partial or mosaic dominance where none of the two contrasting alleles or factors is dominant, e.g. incomplete dominance in 4 ‘O’ clock plant.

Question 69. (i) List three different allelic forms of gene T in human. Explain the different phenotypic expressions, controlled by these three forms. (ii) A woman with blood group A marries a man with blood group O. Discuss the possibilities of the inheritance of the blood group in the following starting with ‘yes’ or ‘no’ for each. (a) They produce children with blood group A only. (b) They produce children, some with 0 blood group and some with A blood group. (Delhi 2012) Answer: (i) In humans, the ABO blood groups are controlled by a gene called T. It has three alleles. These are I A , I B and i. Table showing the genetic basic of blood groups in human population Refer to Answer No. 47.

(ii) (a) No, its not necessary as mother could have a genotype I A I A or I A i. If the genotype is I A I A , all the offsprings would have A blood group, but in the second case, offsprings can have either ‘A’ or ‘O’ blood group as their father has ‘O’ blood group.

(b) Yes, if the mother is of genotype I A i and father is ‘O’ (genotype ii), blood group of some children can be ‘O’ and some can be ‘A’.

(iii) Phenotypic ratio in F 2 -generation. In monohybrid cross – 3:1 In dihybrid cross – 9 : 3 : 3 : 1

(ii) Type of cross-Test cross. Significance The cross is used to determine the genotype of the unknown dominant parent.

(iii) In this test cross, violet and pure white flowers when crossed produce violet and white flowers. Whereas in snapdragon, the F 1 -generation hybrid was pink coloured. F 2 -generation consists of red, pink and white flowers in the ratio of 1 red : 2 pink : 1 white. This is due to incomplete dominance. Similar type of cross can be made for plants with green and yellow pods. Question 72. Write the sex of a human having XXY chromosome With 22 pairs of autosomes. Name the disorder this human suffers from. (2018C) Answer: The sex of a human having XXY chromosomeswith 22 pairs of autosomes is male. The disorder from which this human is suffering is Klinefelter’s syndrome.

Question 73. State the fate of a pair of autosome during gamete formation. (Delhi 2017) Answer: During gamete formation, the homologous pair of autosomes gets separated from each other and moves to different gametes, so that each gamete receives haploid set of chromosomes.

Question 74. Give an example of a human disorder that is caused due to a single gene mutation. (Delhi 2016) Answer: Sickle-cell anaemia is an example of a human disorder that is an caused due to a single gene mutation.

Question 75. Give an example of a sex-linked recessive disorder in humans. (Delhi 2016C) Answer: Haemophilia is a sex-linked recessive disorder in humans.

Question 76. Give an example of an organism that exhibits haplo-diploidy sex-determination system. (Delhi 2016) Answer: Haplo-diploidy sex-determination system is seen in honeybees.

Question 77. Give one example of organism exhibiting female heterogamety. (Outside Delhi 2016C) Or Write the chromosomal basis of sex-determination in birds. (Delhi 2016C) Or Explain the mechanism of sex-determination in birds. (Delhi 2015) Answer: Female heterogamety is exhibited by birds. They have ZW-ZZ type of sex-determination mechanism. In this type, the male is homogametic and the female is heterogametic. Therefore, there are two types of eggs, i.e. with Z and with W and only one type of sperms, i.e. each with Z.

Question 78. Identify the correct statement (i) Females of many birds have a pair of dissimilar ZW-chromosomes, while the males possess a pair of similar 2Z-chromosomes. (ii) Females of many birds have a pair of similar ZZ-chromosomes, while the males possess a pair of dissimilar ZW-chromosomes. (All India 2014C) Answer: The correct statement is (i) Females of many birds have a pair of dissimilar ZW-chromosomes, while the males possess a pair of similar ZZ-chromosomes.

Question 79. Identify and write the correct statement (i) In grasshopper males, two sex chromosomes are X and Y type. (ii) In grasshopper males, there exist XO type of sex-determinants. (All India 2014C) Answer: The correct statement Is (ii) In grasshopper males, there exist XO type of sex-determinants.

Question 80. Identify and write the correct statement (i) Drosophila male has one X and one Y-chromosome. (ii) Drosophila male has two X-chromosomes. (All India 2014C) Answer: The correct statement is (i) Drosophila male has one X and one Y-chromosome.

Question 81. Why do normal red blood cells become elongated and sickle-shaped in structure in a person suffering from sickle-cell anaemia? (Foreign 2014) Answer: In sickle-cell anaemia, substitution of valine in place of glutamic acid in the sixth position of haemoglobin chain occurs. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to the elongated sickle-like structure.

Question 82. Name one autosomal dominant and one autosomal recessive Mendelian disorder in humans. (All India 2010) Answer: Autosomal dominant Mendelian disorder- Huntington’s disease. Autosomal recessive Mendelian disorder-Sickle-cell anaemia.

Question 83. Write the genotype of (i) an individual who is the carrier of sickle-cell anaemia gene, but apparently unaffected and (ii) an individual affected with the disease. (All India 2010) Answer: (i) Hb A Hb s (ii) Hb s Hb s

Question 84. A human being suffering from Down’s syndrome shows trisomy of 21st chromosome. Mention the cause of this chromosomal abnormality. (All India 2010) Or Write the cause of Down’s syndrome in humans. (All India 2010C) Answer: This is due to non-disjunction, i.e. failure of segregation of homologous chromosomes during gamete formation resulting in the gain of an extra copy of chromosome number 21 (21 Trisomy).

Question 85. The son of a haemophilic man may not get this genetic disorder. Mention the reason. (Delhi 2010C) Answer: The gene responsible for haemophilia is located on X-chromosome and males have only single copy of X-chromosome with no alternate normal allele. The son gets X-chromosome from mother only. So, if the female is normal, the son may not get this genetic disorder from male (father).

Question 86. Write the genotypes of the parents of a child suffering from thalassemia. State the cause of this disease. (All India 2019) Answer: The genotypes of the parents of a child suffering from thalassemia are as follows Mother → Th B Th B+ Father → Th B Th B+ Thalassemia is an autosomal-linked recessive disease, which results in reduced rate of synthesis of one of the globin chains of haemoglobin. The disease is controlled by a single pair of allele, Th B and Th B+ . Th B codes for normal B-protein and Th B+ codes for an abnormal B-protein. Only homozygous individuals for Th B+ (Th B+ Th B+ ) show the diseased phenotype.

Question 87. Name a disorder a human suffers from as a result of monosomy of the sex chromosome. Give the karyotype and write the symptoms. (All India 2019) Answer: Monosomy of the sex chromosome in humans results in Turner’s syndrome. The number of chromosomes is 45 (44+ XO).

Symptoms are as follows:

• The affected females are sterile as ovaries are rudimentary.
• Other symptoms include lack of secondary sexual characters, short stature, etc

(ii) Haemophilia is a sex-linked recessive disease. It is transmitted from the carrier female to her sons. From the above pedigree chart, it can be observed that the disease is being transmitted from the carrier female to her daughter (carrier) and son (affected). The carrier daughter transmits this disease to the grandson. This pattern of inheritance is called criss-cross inheritance.

Question 90. A couple with normal vision bears a colourblind child. Work out the cross to show how it is possible and mention the sex of the affected child. (Delhi 2016) Or A colourblind child is born to a normal couple. Work out a cross to show how it is possible. Mention the sex of this child. (Delhi 2014) Answer: Colour blindness is a sex-linked disease which results in the defect in either red or green cone cells of eyes. The gene for this disorder is present on the X-chromosome. Hence, it is carried by normal females that do not express the disease.

Question 91. Differentiate between male and female heterogamety. (Delhi 2015) Answer: Differences between male and female heterogamety are

Male heterogamety	Female heterogamety
Male produces two different types of gametes.	Female produces two different types of gametes.
Example: human male produces gametes with either X or Y-chromosomes.	Example: female birds produce gametes with either Z or W type chromosomes.

Question 92. Why is the possibility of a human female suffering from haemophilia rare? Explain. (Foreign 2014, All India 2012,2013,2014C) Answer: Haemophilia is an X-linked recessive disease. Therefore, the females having haemophilic allele on single X-chromosome do not produce haemophilic phenotype. Females suffer from this disease only if the father is haemophilic and the mother is at least the carrier of disease. Such condition is rare and hence, the human females are rarely haemophilic.

Question 93. Why is pedigree analysis done in the study of human genetics? State the conclusions that can be drawn from it. (All India 2014) Answer: The study of inheritance of genetic traits in several generations of a human family in the form of a family diagram is called pedigree analysis. Inheritance pattern of traits in human beings cannot be studied by crosses. Thus, pedigree analysis is done. Based on the pedigree studies, inheritance of a specific trait, abnormality or disease can be traced.

Question 94. Identify a, b, c, d, e and / in the table given below (All India 2014)

Syndrome	Cause	Characteristics of affected individual	Sex Male/ Female/ Both
Down’s	Trisomy of 21	a (i), (ii)	b
c	XXY	Overall masculine development	d
Turner’s	45 with XO	e (i) (ii)	f

Answer: (a) (i) Short stature individuals with round head and furrowed tongue. (ii) Slow piental development. (b) Both (c) Klinefelter’s syndrome (d) Male (e) (i) Rudimentary ovaries. (ii) Lack of secondary sexual characters. (f) Female

Question 96. Name a blood related autosomal Mendelian disorder. Why is it called Mendelian disorder? How is the disorder transmitted from parents to offspring? (All India 2014C) Answer: A blood related autosomal Mendelian genetic disorder is sickle-cell anaemia. It occurs by the change of a single base pair in the gene, leading to the substitution of glutamic acid by valine at the 6th position of p-globin chain of haemoglobin.

Since, its transmission follows Mendelian principles, it is called Mendelian disorder. Inheritance pattern It is transmitted from parents to the offspring, when both the partners are carriers (heterozygous) of the disease. Refer to the cross on page no. 116.

Question 97. Write the types of sex-determination mechanisms the following crosses show. Give an example of each type. (i) Female XX with male XO. (ii) Female ZW with male ZZ. (Delhi 2014) Answer: (i) The type of sex-determination mechanism shown in female XX and males XO is called male heterogamety. In this case, males are heterogametic with half of the male gametes carrying X-chromosome while the other half being devoid of it, e.g. grasshopper.

(ii) The type of sex-determination mechanism is female heterogamety because female produces two different types of gametes, i.e. Z and W while males are ZZ type, e.g. birds.

Question 98. (i) Colour blindness in humans is a sex-linked trait. Explain with the help of a cross. (ii) In human beings, the sex of the child is determined by the father and not by the mother. Explain. (All India 2014C) Answer: (i) Refer to Answer No. 19. (ii) Refer to Answer No. 24. (1+1)

Give reasons, which explain that haemophilia is (Foreign 2011) (i) sex-linked (ii) caused by X-linked gene. Answer: The pedigree of a family given in the question depicts that mother is normal (XX), while father is haemophilic (X h Y). As haemophilia is a sex-linked disease, F 1 -generation will produce 50% carrier daughters and 50% normal sons. In F 2 -generation, both carrier daughters got married to a normal man and produced 25% diseased (X h Y) and 25% normal son (XY) and 25% carrier (X C X) and 25% normal daughter (XX).

Or (i) (a) It is X-linked trait which is transmitted from an unaffected carrier female to some of the male offsprings. (b) Females rarely become haemophilic as in this cases, the mother has to be at least a carrier and father should be haemophilic.

(ii) Gene for haemophilia is X-linked or present on X-chromosome because male receives this gene from mother. (a) So, a carrier female transmits it to her son. (b) Disease appears more in males because they have only one X-chromosome.

In mutation B, the change in amino acid occurs when codon GAG is changed to GUG because GUG codes for valine, while the original codon GAG codes for glutamic acid. Thus, there will be a change in the haemoglobin structure which would lead to sickle-cell anaemia.

(ii) The normal individual has biconcave, disc-like RBCs, whereas the sufferer has sickle-shaped RBCs.

(iii) It is an autosomal recessive disorder. So, both males and females suffer equally.

Question 102. Name the kind of diseases/disorders and any two symptoms that are likely to occur in humans if (i) Mutation in the gene that codes for an enzyme phenylalanine hydroxylase occurs. (ii) the karyotype is XXY. (All India 2019) Or (i) Name the kind of diseases/disorders that are likely to occur in humans if (a) mutation in the gene that codes for an enzyme phenylalanine hydrolase occurs, (b) there is an extra copy of chromosome 21, (c) the karyotype is XXY. (ii) Mention any one symptom of the diseases/disorders named above. (Foreign 2015) Answer: (i) The following types of diseases are likely to occur in human (a) Phenylketonuria (b) Down’s syndrome (c) Klinefelter’s syndrome

(ii) Symptoms of above diseases are (a) Phenylketonuria Accumulation of phenylketonuria causes mental retardation. (b) Down’s syndrome Affected individuals are short statured with small round head. (c) Klinefelter’s syndrome The individuals are sterile.

Question 103. Explain the mechanism of sex-determination in birds. How does it differ from that of human beings? 2018 Or Differentiate between ‘ZZ’ and ‘XT type of sex-determination mechanisms. (Delhi 2015) Or Explain the sex-determination mechanism in humans. How is it different in birds? (All India 2010) Answer: Differences between XY and ZZ types of sex-determination are as follows

XY type sex-determination (In humans)	ZZ type sex-determination (In birds)
Females are homogametic, while males are heterogametic.	Females are heterogametic, while males are homogametic.
Female produces egg with X-chromosomes only, while male produces sperms with either X or Y-chromosomes Example: humans, Drosophila	Female produces eggs with either Z or W-chromosomes, while male produces sperm with Z-chromosomes. Example:  fish, birds, etc.

Sex-determination in humans Refer to Answer No. 24. Sex-determination in birds Refer to Answer No. 6.

Question 104. During a medical investigation, an infant was found to possess an extra chromosome 21. Describe the symptoms the child is likely to develop later in the life. (Delhi 2017) Or Explain how trisomy of 21st chromosome occurs in humans. List any four characteristic features in an individual suffering from it. (Foreign 2012) Or Name the genetic disorder caused by trisomy of 21st chromosome in a human. Write the diagnostic features of the disorder. (Delhi 2011C) Answer: An additional copy of chromosome number 21 (trisomy of chromosome number 21) in humans results in Down’s syndrome. Following characteristic symptoms are likely to develop in the child suffering from Down’s syndrome

• Short statured with small, round head.
• Furrowed tongue and partially open mouth.
• Broad palm with characteristics palm crease.
• Slow mental, physical and psychomotor development.

Question 105. Both haemophilia and thalassemia are blood related disorders in humans. Write their causes and the difference between the two. Name the category of genetic disorder they both come under. (All India 2017) Answer: Haemophilia and thalassemia both are Mendelian or gene related human disorders. Cause of Haemophilia It is caused due to the absence of antihaemophilic globulin and plasma thromboplastin factor. Cause of Thalassemia It is caused due to mutation or deletion of the genes controlling the formation of globin chains (a and P) of haemoglobin. Differences between haemophilia and thalassemia are as follows

Haemophilia	Thalassemia
Influence on single trait.	Influence on multiple traits.
Inheritance is criss-cross.	Inheritance is straight from both the parents to all the offsprings.

Category of genetic disorder Haemophilia – Sex-linked disease Thalassemia – Autosomal recessive disease

Question 107. Which chromosomes carry the mutant genes causing thalassemia in humans? What are the problems caused by these mutant genes? (Delhi 2015) Or Write the type and location of the gene causing thalassemia in humans. State the cause and symptoms of the disease. How is sickle-cell anaemia different from this disease? (Foreign 2014) Answer: Thalassemia is an autosomal-linked recessive disease, which occurs due to either mutation or deletion of genes, resulting in reduced rate of synthesis of one of the globin chains of haemoglobin. It is associated with the mutation in chromosome 11 or 16 which code for p-chain and a – chain of haemoglobin, respectively. Haemoglobin is the oxygen carrying component of the red blood cells. It consists of two different proteins, an a and a p. If the body does not produce enough of either of these two proteins, the red blood cells do not form properly and cannot carry sufficient oxygen. This results in anaemia that begins in early childhood and lasts throughout the life. For sickle-cell anaemia, Refer to Answer No. 25.

Question 108. Name the phenomenon that leads to situations like ‘XO’ abnormality in humans. How do humans with ‘XO’ abnormality suffer? Explain. (Foreign 2012) Or Name a disorder, give the karyotype and write the symptoms a human suffers from as a result of monosomy of the sex chromosome. (Foreign 2011) Or (i) Name the genetic disorder in a human female having 44 + XO karyotype. Mention the diagnostic features of this disorder. (ii) Explain the cause of such chromosomal disorder. (Delhi 2011c) Answer: XO abnormality or monosomy of X-chromosome represents chromosomal disorder called Turner’s syndrome.

Non-disjunction is responsible for this chromosomal disorder. It is the phenomenon of failure of segregation of the members of homologous pairs of the chromosomes. Such disorder occurs due to the absence of one X-chromosome, i.e. 45 with XO (karyotype). The affected individual has underdeveloped feminine characters. Females are sterile and ovaries are rudimentary.

Question 109. (i) Sickle-cell anaemia in humans is a result of point mutation. Explain. (ii) Write the genotypes of both the parents, who have produced a sickle-celled anaemic offspring. (Delhi 2011) Answer: (i) Point mutation occurs due to change in a single base pair of DNA. Sickle-cell anaemia occurs due to defect caused by the single base substitution at the sixth codon of the P-chain of haemoglobin from GAG to GUG.

This causes substitution of glutamic acid by valine. The defective haemoglobin molecule undergoes polymerisation under low oxygen tension causing sickle-shaped red blood cells.

(ii) The parents must be heterozygotes, i.e. Hb A Hb s and Hb A Hb s to produce a sickle-celled anaemic offspring. Refer to Answer No. 25 and 35.

Question 110. Name a disorder, give the karyotype and write the symptoms where a human male suffers as a result of an additional X-chromosome. (Foreign 2011) Or Name the genetic disorder caused by an extra X-chromosome in a human male. State the diagnostic features of the individual suffering from it. (Delhi 2011C) Answer: It is a chromosomal disorder called Klinefelter’s syndrome, which occurs in males. The affected human males have XXY sex chromosome (47 chromosomes). Karyotype: 44 + XY Symptoms

• Development of feminine characters like breast development.
• Body hair sparse.
• Individual is sterile.

Question 111. (i) Why are grasshopper and Drosophila said to show male heterogamety? Explain. (ii) Explain female heterogamety with the help of an example. (All India 2010) Or Explain the mechanism of sex-determination in insects like Drosophila and grasshopper. (All India 2010) Answer: (i) In male heterogamety, males produce two different types of gametes. In humans and Drosophila, the males have one X and Y chromosome, whereas in grasshopper, the male have only one X-chromosome (XO type). Thus, the males of these organisms show male heterogamety as they produce two types of gametes Either with or without X-chromosome Some gametes with X-chromosome and some with Y-chromosome.

(ii) In some organisms, females produce two different types of gametes. This is termed as female heterogamety. In birds and some reptiles, female has two different sex chromosomes (one Z and one W-chromosome) whereas male has a pair of same chromosome (a pair of Z-chromosome). (11/2)

Question 112. (i) Why are thalassemia and haemophilia categorised as Mendelian disorders? Write the symptoms of these diseases. Explain their pattern of inheritance in humans. (ii) Write the genotypes of the normal parents producing a haemophilic son. (All India 2015) Answer: (i) Thalassemia and haemophilia are categorised as Mendelian disorders because these disorders are due to alteration in a single gene. Also, they are transmitted to offspring through Mendelian principles of inheritance. Symptoms and pattern of inheritance are given below

(a) Thalassemia It is an autosome-linked recessive blood disorder characterised by defect in α, ß or δ-chain resulting in abnormal Hb molecule. Symptom Anaemia: Inheritance Two mutant alleles (one from each parent) must be inherited for an individual to be affected, i.e. homozygous. Heterozygous are carriers and may pass the mutant allele to their children.

(b) Haemophilia It is a sex-linked recessive disorder whose gene is located on X-chromosome. Symptom Prolonged clotting time and internal bleeding, even in a minor injury.

Inheritance The gene is present on X-chromosome, so it is inherited by males as they have a single X-chromosome. Affected males are said to be hemizygous. Females have 2 X-chromosomes, thus their possibility of being affected is rare as the mother of such female has to be at least carrier and father should be haemophilic.

Question 113. (i) Why are colour blindness and thalassemia categorised as Mendelian disorders? Write the symptoms of these diseases seen in people suffering from them. (ii) About 8% of human male population suffers from colour blindness whereas only about 0.4% of human female population suffers from this disease. Write an explanation to show how it is possible. (All India 2015) Answer: (i) The inheritance pattern of colour blindness is same as that of haemophilia. Refer to Answer No. 41.

(ii) Colour blindness is an X-linked recessive trait which shows transmission from carrier female progeny. In males, the defect can appear in heterozygous condition beacause males possess only one X-chromosome whereas in females, it appears in homozygous condition only, which is very rare. Thus, it is more common in males than females.

Question 114. (i) Explain the mechanism of sex-determination in humans. (ii) Differentiate between male heterogamety and female heterogamety with the help of an example of each. (All India 2013) Answer: (i) Refer to Answer No. 24.

(ii) A sex (male or female) is heterogametic, if it has two different sex chromosomes. Male heterogamety The female has two X-chromosomes (XX), while male has only one X-chromosome and at the time of gametogenesis the latter produces two types of gametes, 50% with X-chromosome, while other 50% without X-chromosomes. Heterogametic r tales are of two types

• XX-XY type, e.g. Drosophila, man, etc.
• XX-XO type, e.g. insects like grasshopper. Female heterogamety In some species like birds,’fishes, etc. females are heterogametic, i.e. produce two types of gametes, while males produce only one type of gamete.

Heterogametic females are of two types

• ZO-ZZ type, e.g. butterflies
• ZW-ZZ type, e.g. insects, fish, reptiles, birds, etc.

Question 115. (i) Why is haemophilia generally observed in human males? Explain the conditions under which a human female can be haemophilic. (ii) A pregnant human female was advised to undergo MTP. It was diagnosed by her doctor that the foetus she is carrying has developed from a zygote formed by an XX-egg fertilised by Y carrying sperm. Why was she advised to undergo MTP? (All India 2011) Answer: (i) The genes for haemophilia are present on X-chromosome. A male has only one X-chromosome and bears only one allele for the trait. He is hemizygous for the trait as Y-chromosome does not have a corresponding allele. A female contains two X-chromosomes. She has to be homozygous recessive to be haemophilic. It means her father must be a sufferer and mother must be either a carrier or sufferer to carry forward the disease.

(ii) The zygote will have XXY-chromosomes. It will develop into a male with Klinefelter’s syndrome. Such males are sterile and show feminine characters. That is why, female was advised to undergo MTP.

Question 116. (i) How does a chromosomal disorder differ from a Mendelian disorder? (ii) Name any two chromosomal aberration-associated disorders. (iii) List the characteristics of the disorders mentioned above that help in their diagnosis. (Delhi 2010) Answer: (i) Differences between chromosomal disorders and Mendelian disorders are

Chromosomal disorders	Mendelian disorders
These are caused due to the absence or excess of one or more chromosomes or abnormal arrangement of one/more chromosomes.	These are due to alteration in a single gene.
They are not transmitted as the affected individual is sterile.	They are transmitted to generations through Mendelian principles of inheritance.
Example: Down’s syndrome, Turner’s syndrome.	Example: colour blindness, phenylketonuria.

(ii) Chromosomal disorders Down’s syndrome and Klinefelter’s syndrome.

(iii) Down’s syndrome The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Physical, psychomotor and mental development is also retarded.

Klinefelter’s syndrome It occurs in males, which show overall muscular development, but feminine development also occurs. Such individuals are sterile.

Question 117. Explain the causes, inheritance pattern and symptoms of any two Mendelian genetic disorders. (Delhi 2010) Answer: Two Mendelian genetic disorders are as follows

• Sickle-cell anaemia Refer to Answer No. 25.
• Phenylketonuria It occurs due to defective allele on the autosome. It is inherited from parent, who are heterozygous for the gene to the offspring.

The affected individual lacks an enzyme phenylalanine hydroxylase that converts the amino acid phenylalanine into tyrosine. As a result, phenylalanine gets accumulated in brain and body and gets converted into phenyl pyruvate and other derivatives.

Symptoms Accumulation of these compounds in the brain causes mental retardation. They are also excreted in the urine due to poor absorption by kidney.

(ii) Individual Y-blood groups can be O or A. (iii) I A and I B when stay together, show the phenomenon of codominance and express themselves in the presence of each other. In heterozygous hybrid, when both alternative alleles coexist, both the alleles show their effect and result in the progeny with AB blood group. This is called codominance.

Question 120. Naresh, a haemophilia patient, forbades his daughter to marry Mohan who is also a haemophilia patient. Is Naresh right? Answer: Naresh is right because his daughter can be carrier of haemophilia disease (an X-linked disorder). If she marries a haemophilic person, there are 75% chances that their offspring will also suffer from haemophilia.

Question 121. Avantika’e doctor advised her to undergo MTP because through diagnostic tests she came to know that her foetus has XO chromosomes. Do you think Avantika should undergo MTP? Give reason. Answer: (i) Yes, Avantika should undergo MTP. (ii) The foetus contains XO chromosomes, i.e. one X-chromosome is lacking. It means that the baby will be suffering from Turner’s syndrome. Therefore, MTP is recommended.

Question 122. Prateek was rushed to a nearby hospital after an accident, which had caused too much blood loss. The hospital failed to supply O negative blood for transfusion. Asif, who was attending a patient there, heard about the situation and agreed to donate blood as he had the same blood group. Prateek’s mother initially refused but was later convinced by her daughter’s view. (i) Why cannot O positive blood be transfused into Prateek’s body? (ii) Human blood grouping is an example of? (iii) What values do you find in Prateek’s sister and Asif? Answer: (i) O + blood group contains antigen for Rh factor. Rh – blood lacks the antigen, so if the two blood mix, it will lead to clotting and thus, death of the patient. (ii) Multiple allelism. (iii) Prateek’s sister shows understanding of science and Asif believes in helping a person in need without thinking about which religion or caste he belongs to.

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Practice questions: Principle of Inheritance and Variation

The following are practice questions for Chapter-5 of Class-XII Biology:-“Principle of Inheritance and Variation”. These questions are sourced from previous years board examinations question papers, sample papers issued by CBSE, NCERT exemplar and certain other sources.

• What percentage of gametes produced by an individual with genotype AaBb will be ab?
• Name the law that explains the expression of only one of the parental characters in the F1 generation of a monohybrid cross.
• How many phenotypes of human skin colour are possible if two individuals of intermediate skin colour (AaBbCc) marry?
• How many types of glycoproteins that determine the ABO blood group are found on the surface of RBCs in humans?
• You have read that a single gene controls starch synthesis or size of the starch grains and the seed shape in pea plant. What is the phenotype produced by the genotype Bb? Why?
• Not all character show true dominance. What are the two other possible types of dominance? Give an example of each.
• Why did Mendel choose pea plant for his experiments?
• Explain the law of dominance with the help of a cross.
• Why did Mendel’s work remain unrecognised from 1865-1900? Who rediscovered his work?
• what is the inheritance pattern for coat colour is shown in shouthon cattle?
• What are the genotypes of parents and offspring of each cross?
• A test is performed to know whether the given plant is homozygous dominant or heterozygous. Name the test and phenotypic ratio of this test for a monohybrid cross.
• Can a child have blood group O if his parents have blood group ‘A’ and ‘B’? Explain.
• Some of the characters in humans exhibit multiple allelism. Yet, these characters are controlled by two alleles only. Justify.
• Differentiate between dominant and co-dominant.
• which pod colour is dominant
• The Phenotypes of the individuals of F1 generation.
• Workout the cross
• What type of cross is this?
• Work out the genotype and phenotype of the progeny.
• What principle of Mendel is illustrated through the result of this cross?
• In Pisum sativum tallness is dominant over dwarfness and yellow seeds are dominant over green. Work out a dihybrid cross for the above condition starting with P1 generation. Also, mention the genotypic and phenotypic ratio.
• A particular garden pea plant produces only violet flowers. It may or may not be homozygous dominant for the trait. How would you ensure the genotype? Explain with crosses.
• Define polygenic inheritance? Explain the concept with the help of an example.
• What do you understand by the concept of pleiotropy? Explain the concept with the help of one condition observed in plants and humans.

VSA Type-I  [1 Mark]

• Name the phenomenon and the cell responsible for the development of drones in honeybees.
• Name one autosomal dominant and one autosomal recessive Mendelian disorders in human beings.
• Does not resemble either of the two parents and is in between the two.
• Resemble only one of the two parents.
• Why, in test cross, did Mendel cross a tall pea plant with a dwarf pea plant only?
• In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental types, as experimentally shown by Morgan and his group.
• F1 generation resembles both the parents.
• F1 generation does not resemble either of the parents.

VSA Type-II  [2 Mark]

• Differentiate between multiple alleles and polygenes.
• Bring out the differences between pleiotropy and multiple allelism, with an example for each.
• How does a test cross help in identifying the genotype of the organism? Explain.

SA Type [3 Mark]

• Who proposed the chromosomal theory of inheritance? Point out any two similarities between the behaviour of genes and that of a chromosome.
• In a breeding experiment, a phenotypic ratio of 3:3:3:1 was obtained on crossing a pea plant with green, inflated pods with another pea plant bearing green constricted pods. Write the genotypes of the parents and judge the accuracy of the result, using a punnet square.
• Sickle cell anaemia in humans is a result of point mutation. Explain.
• write the genotype of the normal parents who have produced a sickle cell anaemia offspring.
• A non-haemophilic couple was informed by their doctor, there is a possibility of a haemophilic child to be born to them. Explain the basis on which the doctor conveyed the information. Give the genotypes and phenotypes of all the possible children who could be born to them.
• Persons with Down’s syndrome and those with Klinefelter’s syndrome have 47 chromosomes each, but they show many differences. Explain why?

• The individual X in the 2 nd generation.
• State the possible blood groups of the individual ‘Y’ in the third generation.
• How does the inheritance of this blood group explain codominance?
• Explain the mechanism of sex determination in insects like Drosophila and grasshopper.
• Explain in brief the three different types of thalassaemia.

LA Type [5 Mark]

• A character may or may not be expressed, but they are inherited by every generation. Justify.
• Study the given pedigree chart and answer the questions that follow.

• Is the trait sex-linked or autosomal dominant or autosomal recessive?
• Write the genotypes of parents in generation I.
• Give the genotype of the first child in generation II and that of the first and second child in generation-III.
• A cross between two pink-flowered Snapdragon plants yielded a progeny with red, pink and white-flowered plants. Explain the pattern of inheritance and the phenomenon involved in it. Mention the phenotypic and genotypic ratios in the progeny.
• Give four as to why Drosophila is well suited for lab experiments in genetics.
• What would be the phenotype and genotype of F1 and F2 generations?
• Give the phenotypic ratio of F2 generation.
• List Mendel’s generalisation that can be derived from the above cross.
• Write the symptoms of haemophilia and sickle cell anaemia in humans. Explain how the inheritance pattern of the two disease differs from each other.

Practice-questions based On NCERT Exemplar

Very Short Answer Type 

• Do you think Mendel’s laws of inheritance would have been different if the characters that he chose were located on the same chromosome?
• Enlist the steps of controlled cross-pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.

• In order to obtain the F1 generation, Mendel pollinated a pure-breeding tall plant with a pure breeding dwarf plant. But for getting the F2 generation, he simply self-pollinated the tall F1 plants. Why?
• For the expression of traits,genes  provide only the potentiality and the environment provides the opportunity. Comment on the veracity of the statement.
• How does a mutagen induce mutation? Explain with example.

Short answer type

• In a Mendelian monohybrid cross, the F2 generation shows identical genotypic and phenotypic ratios. What does it tell us about the nature of alleles involved? Justify your answer.
• Why is it that the chances of having a child with Down’s syndrome increase if the age of the mother exceeds forty years?
• A plant with red flowers was crossed with another plant with yellow flowers. If F1 showed all flowers orange in colour, explain the inheritance.
• Why is the frequency of red green colour blindness is many times higher in males than that in the females?
• It is said, that the harmful alleles get eliminated from the population over a period of time, yet sickle cell anaemia is persisting in the human population. Why?
• Discuss the contributions of Morgan and Sturvant in the area of genetics.

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very helpful for my test

sir can we get answers for above questions mainly for pedigree charts which i feel easy to understand

Very much helpful

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Important Questions for CBSE Class 12 Biology Chapter 5 - Principles of Inheritance and Variation 2024-25

• Class 12 Important Question
• Chapter 5: Principles Of Inheritance And Variation

Crucial Practice Questions for CBSE Class 12 Biology Chapter 5: Principles of Inheritance and Variation

Class 12 biology chapter 5 important questions PDF provides the students with well-explained answers to the most important and frequently asked questions of the chapter, such that each of the students can get a more easy way of learning and understanding the chapter. This in turn would help them ace their exams. Class 12 biology principles of inheritance and variation important questions are important for the board as well as entrance exams purpose, such as NEET .

Download CBSE Class 12 Biology Important Questions 2024-25 PDF

Also, check CBSE Class 12 Biology Important Questions for other chapters:

CBSE Class 12 Biology Important Questions
Sl.No	Chapter No	Chapter Name
1	Chapter 1
2	Chapter 2
3	Chapter 3
4	Chapter 4
5	Chapter 5	Principles of Inheritance and Variation
6	Chapter 6
7	Chapter 7
8	Chapter 8
9	Chapter 9
10	Chapter 10
11	Chapter 11
12	Chapter 12
13	Chapter 13
14	Chapter 14
15	Chapter 15
16	Chapter 16

Related Chapters

Boost your Performance in CBSE Class 12 Biology Exam Chapter 4 with Important Questions

Very Short Questions and Answers (1 Marks Questions)

1. Give any two reasons for the selection of pea plants by Mendel for his experiments. 

Ans: The two reasons for the selection of pea plants by Mendel for his experiments are:

(i) Many varieties are present with contrasting forms of characters. 

(ii) They can be easily cross-pollinated as well as self-pollinated. 

2. Name any one plant that shows the phenomenon of incomplete dominance during the inheritance of its flower colour. 

Ans: Dog flower or Snapdragon (Antirrhinum sp.) is the plant that shows the phenomenon of incomplete dominance during the inheritance of its flower colour.

3. Name the base change and the amino acid change, responsible for sickle cell anaemia. 

Ans: The change in base GAG as GUG and substitution of Glutamic acid by valine is responsible for sickle cell anaemia. 

4. Name the disorder with the following chromosome complement. 

(i) 22 pairs of autosomes + X X Y 

Ans: The name of disorders are:

(i) Klinefelter's Syndrome with chromosome complement as 22 pairs of autosomes + X X Y.  

(ii) 22 pairs of autosomes + 21st chromosome + XY. 

Ans: Downs syndrome with chromosome complement as 22 pairs of autosomes + 21st chromosome + XY.

5. A haemophilic man marries a normal homozygous woman. What is the probability that their daughter will be haemophilic? 

Ans: When a haemophilic man marries a normal homozygous woman, is the probability of their daughter being haemophilic is $ 0 $%.

6. A test is performed to know whether the given plant is homozygous dominant or heterozygous. Name the test and phenotypic ratio of this test for a monohybrid cross. 

Ans: A test cross is performed to know whether the given plant is homozygous dominant or heterozygous and 1:1 is the phenotypic ratio of the test cross for a monohybrid cross.

7. Name the phenomena that occur when homologous chromosomes do not separate during meiosis. 

Ans: The name of the phenomenon is non – disjunction that occurs when homologous chromosomes do not separate during meiosis. 

8. Name one trait each in humans & in drosophila whose genes are located on the sex chromosome. 

Ans: The name of traits whose genes are located on the sex chromosome in humans is colourblindness and in drosophila is eye colour.

9. What is meant by aneuploidy? 

Ans: Aneuploidy is the phenomenon of the existing or loss of one or more chromosomes due to failure in the separation of members of a homologous pair of chromosomes during meiosis. 

10. What genetic principle could be derived from a monohybrid cross? 

Ans: The Law of dominance is the genetic principle derived from a monohybrid cross.

11. Which one change is the cause of sickle–cell anaemia? 

Ans: Sickle–cell anaemia is caused due to a point mutation at the 6th position in the B-chain of haemoglobin in which glutamic acid is replaced by valine. 

12. What is a test cross? 

Ans: A test cross is a cross in which offspring with a dominant phenotype is crossed with a homozygous recessive individual to determine the offspring’s genotype for the specific trait. 

13. What is mutagen? Give an example? 

Ans: The physical or chemical agents that cause mutations are called mutagen. For eg x-rays, CNBr etc. 

14. What was the total number of varieties of garden pea which Mendel had taken to start his experiment? 

Ans: The total number of fourteen varieties of a garden pea has been taken by Mendel to start his experiment. 

15. Name any one plant & its feature that shows the phenomena of incomplete dominance? 

Ans: Antirrhinum majus shows the phenomenon of incomplete dominance in flower colour. 

Short Questions and Answers (2 Marks Questions)

1. Identify the sex of the organism as male or female in which the sex chromosome is found as 

(i) ZW in birds 

Ans: ZW in birds: Female 

(ii) XY in Drosophila

Ans: XY in Drosophila: Male

(iii) ZZ in birds  

Ans: ZZ in birds: Female 

(iv) XO in grasshoppers

Ans: XO in grasshopper: Male 

2. Mention two differences between Turner’s syndrome and Klinefelter's syndrome.

Ans: The two differences between Turner’s syndrome and Klinefelter's syndrome is as follows:

Turner’s syndrome	Klinefelter's syndrome
The suffering individual is female.	The suffering individual is male.
It has 45 chromosomes i.e., one X chromosome is less.	It has 47 chromosomes i.e., one extra X chromosome.

3. The human male never passes on the gene for haemophilia to his son. Why is it so? 

Ans: The human male never passes on the gene for haemophilia to his son because the gene for haemophilia is present on the X chromosome. A male has only one X chromosome which he receives from his mother and the Y chromosome from his father. The human male passes the X chromosome to his daughters or female progeny and not to the sons or male progeny. 

4. Mention four reasons why Drosophila was chosen by Morgan for his experiments in genetics. 

Ans: The four reasons for which Morgan has chosen Drosophila for his experiments in genetics are as follows:

(i) Drosophila has a very short life cycle i.e. of 2-weeks.

(ii) It can be grown easily in the laboratory. 

(iii) In single mating it produces a large number of flies. 

(iv) Many hereditary variations have been shown by males and females.

(v) It has only 4 pairs of chromosomes that are distinct in size and shape. 

5. Differentiate between point mutation and frameshift mutations. 

Ans: The difference between point mutation and frameshift mutation is as follows:

Point mutation	Frameshift mutation
It arises due to change in a single base pair of DNA e.g., sickle cell anaemia.	It arises due to deletion or insertion or duplication or addition of one or two bases in DNA.

6. Give any two similarities between the behaviour of genes (Mendel’s factor) during inheritance and chromosomes during cell division. 

Ans: The two similarities  between the behaviour of genes (Mendel’s factor) during inheritance and the behaviour of chromosomes during cell division are as follows:

(i) In diploid cells, the chromosomes are found in pairs like Mendelian factors. 

(ii) The chromosomes of different homologous pairs are assorted independently into gametes during meiosis. This is at random showing parallelism with mendelian factors. 

7. Which law of Mendel is universally accepted? State the law? 

Ans: Mendel’s law of segregation is universally accepted. The law states that – “The two alleles of a gene remain separate and do not contaminate each other in F1 or the hybrid. At the time of gamete formation, two alleles get separated and pair into different gametes”. 

8. How will you find out whether a given plant is homozygous or heterozygous? 

Ans: To test whether a plant is homozygous or heterozygous, a test cross is performed in which an individual is crossed with homozygous recessive for the trait. If a plant is heterozygous, the progeny of testcross consists of tall and dwarf plants in the ratio of 1:1.

If the plant is homozygous, the progeny of testcross will have all tall plants. 

9. Why do sons of a haemophilic father never suffer from this trait? 

Ans: Since haemophilic is a sex-linked character and the gene responsible for haemophilia is present on the X chromosome, it shows criss-cross inheritance i.e., the X chromosome is transferred from father to his daughter and not to his son. Therefore the son of a haemophilic father is never haemophilic. 

10. How is the child affected if it has grown from the zygote formed by an XX-egg fertilized by Y-carrying sperm? What do you call this abnormality? 

Ans: If a child has grown from the zygote formed by XX-egg fertilized by Y-sperm, the child will suffer from Klinefelter syndrome and he will have XXY genotype. The Klinefelter syndrome is characterized by the child’s development of prominent feminine characters such as tall stature with feminised physique, breast development, pubic hair pattern, poor beard growth, & sterility. 

11. The map distance between a certain organisms genes A and B is 4 units, between B and C is 5 units and between C and D is 8 units. Which one of the gene pairs will show more recombination frequency? Give reason.

Ans: Here, C and D will show maximum gene recombination because genes that are linked more closely are having the least frequency of recombination and vice versa. 

12. Give the chromosomal constitution and related sex in each of the following:- 

(i) Turner syndrome 

Ans: Turner syndrome – In Turner syndrome XO is the chromosomal constitution and is female containing 45 chromosomes and lacking in one X-Chromosome. 

(ii) Klinefelter syndrome 

Ans: Klinefelter syndrome – In Klinefelter syndrome XXY is the chromosomal constitution and is male containing 47 chromosomes and has one extra X-chromosome. 

13. What is pedigree analysis? How is it useful? 

Ans: The analysis of case history about the inheritance of a specific trait in several generations of a family is named pedigree analysis. It provides a robust tool that's utilized to trace the inheritance of specific traits or abnormalities or diseases.

14. What are multiple alleles? Give an example? 

Ans: The presence of more than two alleles of a trait is called multiple alleles. E.g. in human beings, four types of blood groups are recognized and their different alleles ${ I }^{ A }$, ${ I }^{ B }$, and ${ I }^{ O }$ of a gene determines the phenotype of four blood groups. 

Long Questions and Answers (3 Marks Questions)

1. A woman with an O blood group marries a man with an AB blood group 

(i) work out all the possible phenotypes and genotypes of the progeny. 

Ans: When a woman with an O blood group marries a man with an AB blood group then- 

All the possible phenotypes of the progeny include blood groups A and B and genotypes of the progeny will be${ I }^{ A }{ i }$and${ I }^{ B }{ i }$ because blood group AB has alleles ${ I }^{ A }{ I }^{ B }$  and blood group O has ${ i }{ i }$ which on the cross gives both types of blood groups A and B while the genotype of progeny will be ${ I }^{ A }{ i }$ and ${ I }^{ B }{ i }$. 

Father’s genes: ${ I }^{ A }{ I }^{ B }$ 

Mother’s genes: ${ i }{ i }$

Therefore, the cross will be

Mother’s genes→ Father’s genes↓	${ i }$	${ i }$
${ I }^{ A }$	${ I }^{ A }{ i }$	${ I }^{ A }{ i }$
${ I }^{ B }$	${ I }^{ B }{ i }$	${ I }^{ B }{ i }$

(ii) Discuss the kind of dominance in the parents and the progeny in this case. 

Ans: In the above-mentioned case, the kind of dominance in the parents and the progeny is that they ( ${ I }^{ A }$ and ${ I }^{ B }$) are equally dominant or co-dominant. In the case of multiple allelism, a gene I exists in three allelic forms, ${ I }^{ A }$, ${ I }^{ B }$ and ${ i }$. 

2. Explain the cause of Klinefelter​’s syndrome. Give any four symptoms shown by the sufferer of this syndrome. 

Ans: The presence of an extra chromosome in males i.e., XXY is the cause of Klinefelter​’s syndrome. The symptoms found in the sufferer of Klinefelter’s syndrome are the development of breast, female type pubic hair pattern, poor beard growth, underdeveloped testes, and tall stature with the feminized physique.

3. In Mendel's breeding experiment on garden peas, the offspring of the ${ F }_{ 2 }$ generation are obtained in the ratio of ${ 25 }$% pure yellow pod, ${ 50 }$% hybrid green pods and ${ 25 }$% green pods. State 

(i) which pod colour is dominant 

Ans: In Mendel's breeding experiment on garden peas, Green pod colour is dominant in the offspring of the   ${ F }_{ 2 }$ generation.

(ii) The Phenotypes of the individuals of the ${ F }_{ 1 }$ generation. 

Ans: Green pod colour is the phenotype of the individuals of the   ${ F }_{ 1 }$ generation. 

(iii) Workout the cross.

Ans: The cross will be shown as:

Phenotypic ratio 3: 1 

Genotypic ratio 1: 2: 1 

4. In Antirrhinum majus a plant with red flowers was crossed with a plant with white flowers. Work out all the possible genotypes and phenotypes of ${ F }_{ 1 }$ and  ${ F }_{ 2 }$ generations, comment on the pattern of inheritance in this case? 

Ans: When Antirrhinum majus, a plant with red flowers, was crossed with a plant with white flowers, the  ${ F }_{ 1 }$ hybrid was pink i.e. a middle colour between red and white will appear which indicates that both red and white are incompletely dominant. When ${ F }_{ 1 }$ individuals were self-pollinated, the   ${ F }_{ 2 }$ generation consists of red, pink and white flowers that appear in the ratio of 1:2:1 respectively. The pattern of inheritance of flower colour in snapdragon or Antirrhinum majus is an example of incomplete dominance.

5. A red-eyed male fruit fly is crossed with a white-eyed female fruit fly. Work out the possible genotype and phenotype of  ${ F }_{ 1 }$ and  ${ F }_{ 2 }$ generation. Comment on the pattern of inheritance in this cross? 

Ans: When a red-eyed male fruit fly is crossed with a white-eyed female fruit fly, the offspring will have both white-eyed male & red-eyed female in the ratio of 1:1  in the   ${ F }_{ 1 }$ generation. In the   ${ F }_{ 2 }$ generation, ${ 50 }$% females will be red-eyed and ${ 50 }$% will be white-eyed, similarly, in males ${ 50 }$% will be red-eyed and ${ 50 }$% will be white-eyed. This result indicates that in fruitflies males transmit their sex-linked characters to their grandson through their daughter; such type of inheritance is called criss-cross inheritance.

6. A man with AB blood group marries a woman with O group blood. 

(i) Work out all the possible phenotypes and genotypes of the progeny. 

Ans. When a man with AB blood group marries a woman with O group blood then, Half the progeny will have blood group A with genotype ${ I }^{ A }  { I }^{ O }$ & half the progeny will have blood group B with genotype  ${ I }^{ B }  { I }^{ O }$.

(ii) Discuss the kind of domination in parents and progeny in this case.

Ans: In this case both the genes ${ I }^{ A }$ and  ${ I }^{ B }$ are dominant over the  ${ I }^{ O }$ gene therefore the progeny shows either blood group A or B. Since in parents both the dominant genes are present together this phenomenon is called codominance. 

7. In a cross made between a hybrid tall and red plant (TtRr) with dwarf & white flower (ttrr). What will be the genotype of plants in the ${ F }_{ 1 }$ generation? 

Ans: When a cross is made between a hybrid tall and red plant (TtRr) with dwarf and white flower (ttrr) plants then TtRr, ttRr, ttRr, and ttRr will be the genotypes of the plants develop in the   ${ F }_{ 1 }$ generation.

8. How sex is determined in human beings? 

Ans: In human beings, all the females bear a pair of X-chromosomes while males have one X-chromosome and one Y-chromosome which is comparatively smaller in size. Thus, in a cross between males and females, there is an equal probability of males and females in progeny and sex is determined based on the presence of a Y-chromosome in the progeny. If a Y-chromosome is present it is male otherwise it is a female child.

9. A smooth seeded and red-flowered pea plant (SsRr) is crossed with a smooth seeded and white-flowered pea plant (Ssrr). Determine the phenotypic and genotypic ratio in  ${ F }_{ 1 }$ progeny? 

Ans: When a   cross is done between smooth seeded and red-flowered pea plant (SsRr) along with a smooth seeded and white-flowered pea plant (Ssrr) then 1:3:3:1 will be the phenotypic ratio in ${ F }_{ 1 }$ progeny i.e., rough seed and red flower =1, smooth seed and red flower =3, smooth seed and white flower =3, and rough seed and white flower =1. The genotypic ratio is   ${ F }_{ 1 }$ progeny will be 1:2:1:2:1:1 i.e., SSRr =1, SsRr =2, SSrr =1, Ssrr =2, ssRr =1, and ssrr =1.

Very Long Questions and Answers (5 Marks Questions)

1. A dihybrid heterozygous round, yellow seeded garden pea (Pisum sativum) was crossed with a double recessive plant. 

(i) What type of cross is this?

Ans: When a dihybrid heterozygous round- yellow seeded garden pea (Pisum sativum) was crossed with a double recessive plant then, this type of cross is known as a dihybrid test cross. 

(ii) Work out the genotype and phenotype of the progeny. 

Ans: Below given is the Work out the genotype and phenotype of the progeny- 

(iii) What principle of Mendel is illustrated through the result of this cross?

Ans: Through the result of the dihybrid test cross Mendel’s principle of independent assortment is illustrated. 

2. In dogs, barking trait is dominant over silent trait & erect ears are dominant over drooping ears. What is the expected phenotypic ratio of offspring when dogs heterozygous for both the traits are crossed? 

Ans: When dogs are heterozygous for both (barking/silent trait and erect ears/drooping ears) the traits are crossed then the expected phenotypic ratio of offspring will be  9 : 3 : 3: 1 where traits for barking & erect ears = 9,  barking & drooping ears =3,  silent & erect ears = 3, and silent & drooping ears =1. 

3. Differentiate between dominance, codominance and incomplete dominance with one example each. 

Ans: The differences between dominance, codominance and incomplete dominance with one example are as follows:

Dominance	Codominance	Incomplete dominance
When a cross is made between two characters in which one character is completely dominant over the other character in the progeny, this phenomenon is called dominance.	If the two equally dominant genes are present together, both of them will be equally expressed, this phenomenon is called codominance.	When a cross is made between two characters of which none of them is completely dominant then an intermediate character develops in the progeny, this phenomenon is called Incomplete dominance.
For eg. When the true-breeding tall pea plant is crossed with the true-breeding dwarf pea plant, all the plants in the  ${ F }_{ 1 }$ generation are tall; this shows that the tall character is dominant over dwarf in the progeny.	For eg. alleles of the blood group, ${ I }^{ A }$ and ${ I }^{ B }$ are dominant over ${ I }^{ O }$ but when both the alleles are present together, both of them will equally express and form a phenotype AB.	For eg. when a cross is made between a red flower & a white flower in a snapdragon flower an intermediate pink colour appears in the progeny.

4. A dihybrid heterozygous tall and yellow pea plant was crossed with the double recessive plant. 

(i) What type of cross is this? 

Ans: When a dihybrid heterozygous tall and yellow pea plant was crossed with the double recessive plant then, this type of cross is known as a test cross.

(ii) Work out the genotype & phenotype of progeny.

Ans: Below given is the work out the genotype & phenotype of progeny- 

Ans: Through the result of testcross Mendel’s Principle of Independent Assortment is illustrated. According to the principle, in the inheritance of contrasting characters, the factors of each pair of characters segregate independently of the factors of the other pair of characters. 

Vedantu’s Important Questions of Chapter 5 Biology Class 12

Vedantu has created a PDF of important questions on the principles of inheritance and variation in Class 12 biology.

The PDF provides a simplified explanation of major topics, making it easier for students to understand and clear their doubts.

It offers a wholesome understanding of the chapter, helping students ace their biology exams.

The PDF is available for free download on Vedantu's platform, making education accessible to all students.

The questions in the PDF cover all the major parts and points of the chapter, serving as a summary for students.

It provides a basic idea of the answer-writing pattern in board exams, aiding students in exam preparation.

The PDF can be used as last-minute revision notes to enhance remembrance of the topics.

It is easily accessible and portable, allowing students to study on any device or take printouts for convenience.

Vedantu also offers live classes, which further support students in learning and understanding the concepts effectively.

Class 12 Biology Chapter 5 Important Questions - Summary

Heredity can be defined as a mechanism of transfer heritable traits and genes from parents to their progeny.

Genetics is the branch of biology that discusses inheritance and variation concepts and mechanisms.

Inheritance is the basis of inheritance and characteristics are passed down from the parents to the offspring through this process. The continuity of the gene pool is preserved by the inheritance mechanism.

Genes are found on chromosomes and are the fundamental unit of inheritance.

Among individuals of one species, variation exists. Variation can happen due to recombination, crossing over, environmental effects, and mutation on the expression of genes that are found on chromosomes.

Mendel's Law of Inheritance:

1. Law of Dominance States That:

Characters are regulated by discrete units that are called factors.

Factors often emerge in pairs.

One member of a pair dominates the other in a distinct pair of factors.

2. Law of Segregation States That:

Each of the alleles gets separated during the process of meiosis, at the time of gamete formation. In this process, there occurs no blending and also the characters are found to be passed to distinct gametes. The production of homozygotes can be done using only a single kind of gametes whereas heterozygotes are produced with the help of two distinct kinds of gametes.

3. Law of Independent Assortment States That:

The law specifies that 'when two pairs of characteristics are mixed in a hybrid, the segregation of one pair of characters is independent of the other pair of characters.' Two new combinations are produced in Dihybrid cross, round green & wrinkled yellow due to an independent assortment of seed color, i.e. yellow and green and seed shape characteristics, i.e. round, wrinkled.

Chromosomal Theory of Inheritance:

Sutton and Boveri accepted the findings of Mendel and claimed that the carrier of genes is chromosomes.

Chromosomes exist as a homologous pair and a gene's two alleles are found at the same location on the homologous pair of chromosomes.

In the course of gamete formation, homologous chromosomes differentiate during meiosis.

Chromosomes independently segregate and assort.

Gametes pair up and produce the progenies with a diploid number of chromosomes, which are similar to the parents. The fusion of gametes occurs during fertilization.

Morgan worked extensively on fruit flies, Drosophila melanogaster, and gave experimental arguments to confirm the chromosomal theory of inheritance.

Linkage and Recombination:

The physical association of chromosome-located genes is known as linkage.

In a dihybrid cross, If two of the genes are closely related or situated on the very same chromosome, then it is observed that the parental combination is way more common than recombinants or non-parental combinations.

The recombination and linkage do vary on the distance present between the pair of genes. As the distance between the genes increases, the probability of recombination also increases.

Sex Determination:

In various species, there are various sex determination mechanisms involved.

First, Henking noticed the X chromosome and called it the X body.

The chromosomes that determine sexual character formation are referred to as sex chromosomes and the remaining chromosomes are referred to as autosomes.

If the male develops two distinct forms of gamete then It is classified as male heterogamety. Examples may include grasshoppers, humans, drosophila, etc.

If the female develops two distinct forms of gamete then It is termed as female heterogamety. Examples may include birds.

Any modification in the DNA sequence is considered a mutation. Viable mutations are observed to undergo inheritance from one generation to another.

This process of alteration in the DNA sequence might affect both the genotype and an organism's phenotype.

It is associated with different disorders, although not all mutations are harmful.

The mutation results in modifications such as deletion, addition, replication, replacement, etc. The significant cause of cancer is mutation.

Genetic Disorders:

Genetic disorders can usually be divided into two groups, Mendelian and Chromosomal disorders.

1. Mendelian Disorders:

Mendelian disorders occur due to single gene modification.

As per Mendel's rule, it follows the same inheritance pattern.

Pedigree Analysis can be used to know the pattern of inheritance and also decide whether the trait is dominant or recessive.

Sickle cell anaemia, Muscular dystrophy, Colour blindness, Thalassemia,Cystic fibrosis, Phenylketonuria are few of the examples of mendelian disorders.

2. Chromosomal Disorders:

Chromosomal diseases are diseases that occur due to chromosomes’ absence, excess, or irregular arrangement.

There are two types of chromosomal disorders:

Aneuploidy - Gain or loss of a chromosome or more. It occurs due to the chromatid segregation failure during meiosis anaphase.

Polyploidy - It is commonly present in plants. This occurs in an increase in the number of chromosomes.

Examples of chromosomal disorders may include Turner’s syndrome, Down's syndrome, and others.

Conclusion:

Class 12 biology principles of inheritance and variation important questions covered all the crucial points. We discussed about Mendel’s Laws of Inheritance, Chromosomal Theory of Inheritance, Linkage and Recombination, Mutation, Sex Determination and Genetic Disorders. All these concepts are highly important from both the exam point of view and the entrance exams.

Important Related Links for CBSE Class 12 Biology

CBSE Class 12 Biology Study Materials

The principle of inheritance and variation is a fundamental concept in biology that explores how traits are passed from one generation to another and the factors that contribute to genetic diversity. Vedantu's collection of important questions on this topic provides a valuable resource for Class 12 biology students to enhance their understanding and preparation for exams. These questions cover a wide range of topics, including Mendelian genetics, sex determination, genetic disorders, DNA replication, and genetic engineering. By practicing these questions, students can reinforce their knowledge, improve their problem-solving skills, and gain confidence in tackling biology examinations. Vedantu's comprehensive question bank is a valuable tool for students aiming to excel in the principle of inheritance and variation.

FAQs on Important Questions for CBSE Class 12 Biology Chapter 5 - Principles of Inheritance and Variation 2024-25

Q1. Why did Morgan choose Drosophila as the Experimental Material for his Studies in Genetics? 

Ans: The reasons for Morgan choosing Drosophila as the experimental material for conducting studies in genetics include: 

Drosophila has a very short life cycle of only two weeks

It can be easily grown under laboratory conditions

In a single mating, Drosophila can produce a large number of offsprings

Drosophila comprises of only four pairs of chromosomes that are distinct in size and shape

The male and female Drosophila display a wide range of heredity variations

Q2. What are the differences between Klinefelter’s and Turner’s Syndrome?

Ans: Both Turner’s and Klinefelter’s syndrome display anomaly in the number of sex chromosomes. However, there are certain differences between the two syndromes that are highlighted below. 

Turner’s syndrome is characterised by the deficit of an  X chromosome. This occurs in female individuals and the total number of chromosomes in the individual is 45. Turner’s syndrome is denoted by 45, X0. 

Klinefelter’s syndrome, on the other hand, is the presence of an extra X chromosome in males. The individual affected here is male and the total number of chromosomes is 47. This syndrome is denoted by 47, XXY

Q3. Why does the Human Male never Pass the Gene for Haemophilia to his Son?

Ans: Haemophilia is an X-chromosomal genetic disorder, i.e., the haemophilic gene on humans is present on the X chromosome. This disorder impairs the ability of the human body to clot blood, in case of an injury. A human male has only one X chromosome, which is inherited from the mother during the process of reproduction while the Y chromosome is obtained from the father. As such, the human male the X chromosome on to the daughters, (characterised by XX) but never on to the sons (characterised by XY). 

Q4. Why should you refer to important questions of Biology Class 12 Chapter 5 by Vedantu? 

Ans: The Class 12 Biology Chapter 5 Principles of Inheritance and Variation Important Questions by Vedantu have been handpicked by the subject experts. While studying the chapter or undergoing a quick recap before the exams the important questions of Biology Class 12 Chapter 5 can prove to be highly beneficial. These important questions encompass all the important topics of the chapter. Moreover, the important questions have also been arranged according to the marks they carry and provided with adept answers. So, go through the important questions of Class 12 Biology Chapter 5 today!

Q5. How are the alleles of a gene different from each other? What is its importance?

Ans: As discussed in Chapter 5 Principles of Inheritance and Variation of Class 12 Biology, the pair of alleles of a gene are different from each other even though their difference is not observed in the phenotype or the traits such as blood type and eye colour. The difference is very minute in the form of the absence or presence of a molecule (mutations in a segment DNA). The Alleles are significant because it is through their presence that variations are visible in organisms.

Q6. What is the study of inheritance and variation called?

Ans: The chapter discusses that the study of inheritance and variation is called Genetics. In simple words, one of the aspects of genetics involves the scientific study of variations that are inherited from the parent to the progeny. The concept of inheritance and variation can be understood with the help of a common example. Many times we notice that children have several features that are similar to their parents because they have 'inherited' these features from their parents. Similarly, the children don't look exactly identical to their parents because of a 'variation' in their genes. 

Q7. How far are the genes and environment responsible for expression of a particular trait?

Ans: The chapter explains that both the genes and environment are responsible for the expression of traits. The inherited genes act as messages in our DNA which play a major role in determining the traits of an individual and the expression of these traits. Similarly, environmental factors such as food, temperature, humidity levels, oxygen, light etc. influence the expression of the traits present in an organism's genes. The environmental factors also affect an animal's phenotype or observable traits such as blood type, height and eye colour.

Q8. What is variation according to  Chapter 5 Principles of Inheritance and Variation of Class 12 Biology?

Ans: As discussed in the chapter, the organisms, even from the same species are not identical and have several differences in physiology, genetics,  behavioural traits, and so on. These differences that make the progeny different from the parent within the same species is referred to as Variation. Thus, in simple words, Variation is the process through which characters are passed to the progeny from the parent. Variation occurs due to several reasons such as environmental factors, reshuffling of genes, mutation and recombination. 

These solutions are available on Vedantu's official website( vedantu.com ) and mobile app free of cost.

Q9. What are the important questions of Chapter 5 Principles of Inheritance and Variation of Class 12 Biology?

Ans: You can access important questions of Chapter 5 Principles of Inheritance and Variation of Class 12 Biology by referring to Vedantu's Important Questions for this chapter. By thoroughly preparing these questions, you will be able to cover the most important topics of the chapter and score well. These questions have been prepared after analyzing the previous year questions and the latest syllabus. Thus, these questions will help you to clear the Biology exam with flying colours.

CBSE Class 12 Biology Important Questions

Cbse study materials.

Class 12 Biology Case Study of Chapter 6 Molecular Basis of Inheritance

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In Class 12 Boards there will be Case studies and Passage Based Questions will be asked, So practice these types of questions. Study Rate is always there to help you. Free PDF Downloads of CBSE Class 12 Biology Chapter 6 Molecular Basis of Inheritance Case Study and Passage Based Questions with Answers were Prepared Based on the Latest Exam Pattern. Students can solve Class 12 Biology Case Study Questions Molecular Basis of Inheritance  to know their preparation level.

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In CBSE Class 12 Biology Paper, There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Molecular Basis of Inheritance Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 12 Biology  Chapter 6 Molecular Basis of Inheritance

Case Study/Passage-Based Questions

Case Study 1: In prokaryotes, DNA is circular and present in the cytoplasm but in eukaryotes, DNA is linear and mainly confined to the nucleus. DNA or deoxyribonucleic acid is a long polymer of nucleotides. In 1953, the first correct double helical structure of DNA was worked out by Watson and Crick. Based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin. It is composed of three components, i.e., A phosphate group, deoxyribose sugar, and a nitrogenous base. Different forms of DNA are B-DNA, Z-DNA, A-DNA, C-DNA, and D-DNA.

(i) Name the linkage present between the nitrogen base and pentose sugar in DNA.

(a) Phosphodiester bond

(b) Glycosidic bond

(c) Hydrogen bond

(d) None of these

Answer: (b) Glycosidic bond

(ii) The double helix structure of DNA was proposed by

(a) James Watson and Francis Crick

(b) Earwin Chargaff

(c) Federick Griffith

(d) Hershey and Chase

Answer: (a) James Watson and Francis Crick

(iii) The double chain of B-DNA is coiled in a helical fashion. The spiral twisting of the B-DNA duplex produces

(a) right and left part

(b) major and minor grooves

(c) upper and lower sides

(d) linear and circular part.

Answer: (b) major and minor grooves

(iv)  Assertion:  The two strands of DNA helix have a uniform distance between them. Reason: A large-sized purine is always paired opposite to a small-sized pyrimidine.

(a) Both assertion and reason are true and reason is the correct explanation of assertion.	(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.	(d) Both assertion and reason are false.

Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion

 (v) Which of the following describes the structure of B-DNA?

(a) Parallel	5
(b) Anti-parallel	10
(c) Parallel	15
(d) Anti-parallel	20

Answer: (b)

Case Study 2: The process of translation requires the transfer of genetic information from a polymer of nucleotides to synthesize a polymer of amino acids. The relationship between the sequence of amino acids in a polypeptide and the nucleotide sequence of DNA or mRNA is called genetic code. George Gamow suggested that in order to code for all the 20 amino acids, code should be made up of three nucleotides.

What is the process by which a polymer of nucleotides is used to synthesize a polymer of amino acids? A) Replication B) Transcription C) Translation D) Mutation

What is the relationship between the sequence of amino acids in a polypeptide and the nucleotide sequence of DNA or mRNA known as? A) Genetic Translation B) Genetic Mutation C) Genetic Replication D) Genetic Code

Who suggested that the genetic code should be made up of three nucleotides? A) James Watson B) Francis Crick C) George Gamow D) Rosalind Franklin

How many nucleotides are required to code for one amino acid in the genetic code? A) One B) Two C) Three D) Four

What is the main reason that three nucleotides are used to code for each amino acid? A) To ensure replication accuracy B) To allow for more combinations and code for all 20 amino acids C) To facilitate faster transcription D) To prevent mutations

Which of the following molecules carries the genetic information from DNA to the ribosome for translation? A) tRNA B) rRNA C) mRNA D) DNA

Hope the information shed above regarding Case Study and Passage Based Questions for Class 12 Biology Chapter 6 Molecular Basis of Inheritance with Answers Pdf free download has been useful to an extent. If you have any other queries about CBSE Class 12 Biology Molecular Basis of Inheritance Case Study and Passage Based Questions with Answers, feel free to comment below so that we can revert back to us at the earliest possible. By Team Study Rate

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Principles of Inheritance and Variation Class 12 Important Questions with Solutions PDF

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An important topic included in the Class 12 Biology subject is Principles of Inheritance and Variation. You must be thorough with this chapter as various questions are asked from it in the board exam. For your assistance, we provide the Principles of Inheritance and Variation class 12 important questions with solutions on the SelfStudys website. With the practice of these questions on a daily basis, you can develop different problem-solving strategies to tackle them in an effective manner. 

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12th Class Biology Principle Of Inheritance And Variation Question Bank

Done mcqs - principles of inheritance and variation total questions - 195.

question_answer 1) Two crosses between the same pair of genotypes of phenotypes in which the sources of the gametes are reversed in one cross is known as:

A) Test cross done clear

B) Dihybrid cross done clear

C) Reverse cross done clear

D) Reciprocal cross done clear

question_answer 2) The total number of progenies obtained through dihybrid cross of Mendel is 1280 in F2 generation. How many are recombinants?

A) 240 done clear

B) 360 done clear

C) 480 done clear

D) 720 done clear

What is shown in the following figure?

A) Steps in making a selfing in a pea plant done clear

B) Steps in making a cross in a lotus plant done clear

C) Steps in making a cross in a pea plant done clear

D) Steps in making a cross in a rose plant done clear

question_answer 4) In Mendel's experiments with garden pea, round seed shape (RR) was dominant over wrinkled seeds (rr), yellow cotyledon (YY) was dominant over green cotyledon (yy). What are the expected phenotypes in the \[{{F}_{2}}\] generation of the cross \[RRYY\text{ }\times \text{ }rryy\text{ }?\]

A) Only round seeds with green cotyledon done clear

B) Only wrinkled seeds with yellow cotyledons done clear

C) Only wrinkled seeds with green cotyledons done clear

D) Round seeds with yellow cotyledons, and wrinkled seeds with yellow cotyledons done clear

question_answer 5) How many different kinds of gametes will be produced by a plant having the genotype AA Bb CC ?

A) Three done clear

B) Four done clear

C) Nine done clear

D) Two done clear

question_answer 6) The possible blood group of children born to parents having A and AB groups are :

A) 0, A done clear

B) A, B, AB done clear

C) 0, A, B done clear

D) 0, A, B, AB done clear

question_answer 7) In Mirabilis jalapa, the number of \[{{F}_{2}}\] red flowered plants in a cross of red flowered x white flowered would be :

A) 1 done clear

B) 2 done clear

C) 3 done clear

D) 4 done clear

What type of cross is shown in the following figure?

A) Diagrammatic representation of dihybrid cross done clear

B) Diagrammatic representation of trihybrid cross done clear

C) Diagrammatic representation of monohybrid cross done clear

D) Diagrammatic representation of test cross done clear

question_answer 9) A common test to find the genotype of a hybrid is by :

A) Crossing of one \[{{F}_{2}}\] progeny with female parent done clear

B) Studying of sexual behaviour of \[{{F}_{1}}\] progenies done clear

C) Crossing of one \[{{F}_{1}}\] progeny with male parent done clear

D) Crossing of one \[{{F}_{2}}\] progeny with male parent done clear

question_answer 10) One of the parents of a cross has mutation in its mitochondria. In that cross, the parent is taken as male. During segregation of \[{{F}_{2}}\] progenies that mutation is found in :

A) One third of the progenies done clear

B) None of the progenies done clear

C) All of the progenies done clear

D) Fifty per cent of the progenies done clear

question_answer 11) In the ABO system of blood groups, if both antigens are present but no antibody, the blood group the individual would be :

A) B done clear

B) 0 done clear

C) AB done clear

D) A done clear

question_answer 12) Extranuclear inheritance is a consequence of presence of genes in :

A) Mitochondria and chloroplasts done clear

B) Endoplasmic reticulum and mitochondria done clear

C) Ribosomes and chloroplasts done clear

D) Lysosomes and ribosomes done clear

question_answer 13) Which one of the following characters studied by Mendel in garden pea was found to be dominant?

A) Green seed colour done clear

B) Terminal flower position done clear

C) Green pod colour done clear

D) Wrinkled seed done clear

question_answer 14) In a given plant red colour (R) of fruits is dominant over white fruit (r); tallness (T) is dominant over dwarfness (t). If a plant with genotype RRTt is crossed with a plant of genotype rrtt, what will be the percentage of tall plants with red fruits in the next generation?

A) 100% done clear

B) 25% done clear

C) 50% done clear

D) 75% done clear

question_answer 15) If a dwarf pea plant was treated with gibberellic acid, it became a tall, as tall pea plants. If these pea plants are crossed with pure tall pea plants, what will be the phenotypic ratio in \[{{F}_{1}}\]generation?

A) All dwarf plants done clear

B) 50% tall and 50% dwarf plants done clear

C) 75 % tall and 25 % dwarf plants done clear

D) 100% tall plants done clear

question_answer 16) Red (dominant) flowered heterozygous crossed with white flower :

A) \[350\text{ }-\text{ }red\text{ }:\text{ }350\text{ }\tilde{\ }\text{ }white\] done clear

B) \[450\text{ }-\text{ }red\text{ }:\text{ }250\text{ }\tilde{\ }\text{ }white\] done clear

C) \[380\text{ }-\text{ }red\text{ }:\text{ }250\text{ }\tilde{\ }\text{ }white\] done clear

D) None of the above done clear

question_answer 17) A tall plant was grown in nutrient deficient soil and remained dwarf. When it is crossed with dwarf plant then :

A) All hybrid plants are dwarf done clear

B) All hybrid plants are tall done clear

C) 50% tall and 50% of dwarf done clear

D) 75% tall and 25% dwarf done clear

question_answer 18) A pure tall and a pure dwarf plant were crossed to produce offspring. Offsprings were self crossed, then find out the ratio between true breeding tall to true breeding dwarf?

A) 1 : 1 done clear

B) 3 : 1 done clear

C) 2 : 1 done clear

D) 1 : 2 : 1 done clear

question_answer 19) Cross between unrelated group of organisms is called :

A) Hybrid done clear

B) Test cross done clear

C) Back cross done clear

D) Heterosis done clear

Cytoplasmic inheritance is due to :

(1) Mitochondria and Chloroplast

(2) Cilia and Flagella

(3) Cytoplasmic particles

(4) Cell wall and Cell coat

A) 1, 2 and 3 are correct done clear

B) 1 and 2 are correct done clear

C) 2 and 4 are correct done clear

D) 1 and 3 are correct done clear

question_answer 21) Mating of an organism to a double recessive in order to determine whether it is homozygous or heterozygous for a character under consideration is called :

A) Reciprocal cross done clear

C) Dihybrid cross done clear

D) Back cross done clear

What is depicted in the following cross?

A) Diagrammatic representation of test cross done clear

B) Diagrammatic representation of out cross done clear

C) Diagrammatic representation of reverse cross done clear

D) Diagrammatic representation of dihybrid cross done clear

question_answer 23) The phenotypic ratio in the \[{{F}_{2}}\] generation of a dihybrid cross is :

A) 9 : 3 : 3 : 1 done clear

B) 1 : 2 : 2 : 4 : 1 : 2 : 1 : 2 : 1 done clear

C) 7 : 1 : 1 : 7 done clear

D) 1 : 2 : 3 : 4 done clear

question_answer 24) A woman is married for the second time. Her first husband was ABO blood type A, and her child by that marriage was type O. Her new husband is type B and their child is type AB. What is the woman's ABO genotype and blood type?

A) \[{{I}^{A}}{{I}^{O}}\]; Blood type A done clear

B) \[{{I}^{A}}{{I}^{B}}\]; Blood type AB done clear

C) \[{{I}^{B}}{{I}^{O}}\]; Blood type B done clear

D) \[{{I}^{O}}{{I}^{O}}\]; Blood type O done clear

question_answer 25) Codominance is depicted by

A) B blood group done clear

B) AB blood group done clear

C) O blood group done clear

D) A blood group done clear

The ABO blood grouping in human beings is an example for :

(i) Dominance

(ii) Incomplete dominance

(iii) Co-dominance

(iv) Multiple alleles

A) (i) and (ii) only done clear

B) (ii), (iii) and (iv) done clear

C) (i) (ii) and (iv) done clear

D) (iii) and (iv) only done clear

question_answer 27) Which of the following genotypes does not produce an sugar polymer on the surface of the RBC ?

A) \[{{I}^{A}}{{I}^{A}}\] done clear

B) \[I{{i}^{B}}\] done clear

C) \[{{I}^{A}}{{I}^{B}}\] done clear

D) ii done clear

question_answer 28) Inheritance of flower colour is an example of incomplete dominance which is seen in :

A) Antirrhinum done clear

B) Pisum done clear

C) Solanum done clear

D) Hibiscus done clear

question_answer 29) Phenotypic ratio in plant Snapdragon in \[{{F}_{2}}\] is :

B) 2 : 1 done clear

C) 3 : 1 done clear

question_answer 30) Test cross is used to :

A) Check heterozygosity in \[{{F}_{1}}\] generation done clear

B) Check heterozygosity in \[{{F}_{2}}\] generation done clear

C) Check independent assortment in \[{{F}_{2}}\] generation done clear

D) Check segregation in \[{{F}_{2}}\] generation done clear

question_answer 31) The ultimate biological unit which controls heredity is called :

A) Genome done clear

B) Chromosome done clear

C) Genotype done clear

D) Gene done clear

question_answer 32) For making important contributions in respect of the nature of genes, the Nobel prize was awarded :

A) T.H. Morgan done clear

B) de Vries done clear

C) H.J. Muller done clear

D) Darwin done clear

question_answer 33) A pea plant parent having violet coloured flowers with unknown genotype was crossed with a plant having white coloured flowers, in the progeny 50% of the flowers were violet and 50% were white. The genotypic constitution of the parent having violet coloured flowers was:

A) Homozygous done clear

B) Merozygous done clear

C) Heterozygous done clear

D) Hemizygous done clear

Find out the correct option regarding the following cross?

A) Monohybrid cross in pea plant done clear

B) Trihybrid cross in pea plant done clear

C) Out cross in pea plant done clear

D) Dihybrid cross in pea plant done clear

question_answer 35) ABO blood group is based on :

A) Co-dominance done clear

B) Incomplete dominance done clear

C) Epistasis done clear

D) Multiple allele done clear

question_answer 36) Test cross of dihybrid ratio is 1 : 1 : 1 : 1. It proves that :

A) \[{{F}_{1}}\] hybrid produces four different progenies done clear

B) \[{{F}_{2}}\] hybrid is homozygous done clear

C) Two different progenies are produced by \[{{P}_{1}}\] parents done clear

D) \[{{F}_{2}}\] hybrid is heterozygous done clear

question_answer 37) If \[{{F}_{1}}\] generation has all tall progenies and ratio of \[{{F}_{2}}\] generation is 3 : 1 (Tall : Dwarf), then it proves:

A) Law of independent assortment done clear

B) Law of segregation done clear

C) Law of dominance done clear

D) Incomplete dominance done clear

question_answer 38) How many pairs of contrasting characters in pea pod were chosen by Mendel :

A) 3 done clear

B) 5 done clear

C) 7 done clear

D) 9 done clear

question_answer 39) If a cross between two individual produce offsprings with 50% dominant character [A] and 50% recessive character [A] the genotype of parents are :

A) Aa AA done clear

B) Aa aa done clear

C) AA aa done clear

D) AA Aa done clear

question_answer 40) When yellow round heterozygous pea plants are self-fertilized, the frequency of occurrence of RrYY genotype among the offsprings is

A) 9/16 done clear

B) 3/16 done clear

C) 2/16 done clear

D) 1/16 done clear

question_answer 41) In an organism, tall phenotype is dominant over recessive dwarf phenotype, and the alleles are designate as T and t, respectively. Upon crossing two different individuals, total 250 offsprings were obtained. out of which 124 displayed tall phenotype and rest were dwarf. Thus, the genotype of the parents was

A) \[TT\times TT\] done clear

B) \[TT\times tt\] done clear

C) \[Tt\times Tt\] done clear

D) \[Tt\times tt\] done clear

question_answer 42) In a monohybrid cross between two heterozygous individuals, the number of pure homozygous individual? obtained in \[{{F}_{1}}\] generation is

A) 2 done clear

B) 4 done clear

C) 6 done clear

D) 8 done clear

question_answer 43) A woman with blood type 'O' has a child with blood type 'O'. If she claims a friend of hers with blood group 'A' as the father of the child, then the genotype of the father would be

A) \[{{I}^{O}}{{I}^{O}}\] done clear

B) \[{{I}^{A}}{{I}^{B}}\] done clear

C) \[{{I}^{A}}{{I}^{O}}\] done clear

D) \[{{I}^{A}}{{I}^{O}}\] done clear

question_answer 44) A woman with straight hair mates with a man with curly hair who is known to be heterozygous for that trait. What is the chance that their first child will have curly hair?

A) No chance done clear

B) One in two done clear

C) It is certain done clear

D) One in four done clear

question_answer 45) Which of the following crosses and resultant phenotype ratios are mismatched?

A) \[Tt\times Tt-3\,:\,1\] done clear

B) \[tt\times Tt-2\,;\,1\] done clear

C) \[Tt\,\,Yy\,\,\times \,\,ttyy\,\,-\,\,1\,\,:\,\,1\,\,:\,\,1\,\,:\,\,1\] done clear

D) \[Tt\,Yy\,\times \,\,TtYy\,\,\,-\,9\,\,:\,\,3\,\,:\,\,3\,\,:\,\,\,1\] done clear

question_answer 46) A man having the genotype EEFfGgHH can produce P number of genetically different sperms, and a woman of genotype IuLLMmNn can generate Q number of genetically different eggs. Determine the values of P and Q

A) P = 4, q = 4 done clear

B) P = 4, q = 6 done clear

C) P = 8, q = 4 done clear

D) P = 8, q = 8 done clear

question_answer 47) An organism, tall phenotype is dominant over recessive dwarf phenotype, and the alleles are designated as T and t, respectively. Upon crossing two different individuals, total 250 offsprings were obtained. out of which 124 displaced tall phenotype and rest were dwarf. Thus, the genotype of the parent; were

A) \[TT\,\,\,\times \,\,\,TT\] done clear

B) \[TT\,\,\,\times \,\,\,tt\] done clear

C) \[Tt\,\,\,\times \,\,\,Tt\] done clear

D) \[Tt\,\,\,\times \,\,\,tt\] done clear

question_answer 48) When yellow round heterozygous pea plants are self-fertilized, the frequency of occurrence of RrYY genotype, among the offsprings is

question_answer 49) ABO blood groups are determined by three different alleles. How many genotypes and phenotypes are possible?                                                                              

Genotype	Phenotype
3	1

Genotype	Phenotype
6	4

Genotype	Phenotype
4	6

Genotype	Phenotype
9	7

question_answer 50) In a monohybrid cross between two heterozygous individuals, the number of pure homozygous individuals obtained in \[{{F}_{1}}\] generation is

question_answer 51) In Mendel's seven contrasting traits of pea total number of colours tested by him was

B) 3 done clear

C) 4 done clear

D) 5 done clear

question_answer 52) Which of the following statements is correct?

A) Each back cross is a test cross. done clear

B) Each test cross is a back cross. done clear

C) Crossing \[{{F}_{2}}\] with \[{{F}_{1}}\] is a test cross. done clear

D) Crossing \[{{F}_{2}}\] with \[{{P}_{1}}\] is called a test cross. done clear

question_answer 53) If a heterozygous tall plant is crossed with a homozygous dwarf plant, the proportion of dwarf progeny will be

A) 25% done clear

B) 50% done clear

C) 75% done clear

D) 100% done clear

question_answer 54) An allele is

A) Another word for gene done clear

B) A homozygous genotype done clear

C) A heterozygous genotype done clear

D) One of the several possible forms of gene done clear

question_answer 55) The graphical representation to calculate the probability of all possible genotypes of offsprings in a genetic cross was developed by

A) Gregor Mendel done clear

B) Kornberg done clear

C) Har Gobind Khorana done clear

D) Reginald C. Punnett done clear

question_answer 56) Choose the wrong statement from the following.

A) Failure of segregation of chromatids during cell division results in aneuploidy done clear

B) Additional copy of 'X' chromosome in males results in Klinefelter's syndrome done clear

C) Closely located genes in a chromosome always assort independently resulting in recombinants done clear

D) According to Mendel, recessive character never blends in heterozygous condition done clear

question_answer 57) In garden pea, round shape of seeds is dominant over wrinkled shape. A pea plant heterozygous for round shape of seed is selfed and 1600 seeds produced during the cross are subsequently germinated. How many seedings would have the parental phenotype?

A) 400 done clear

B) 1600 done clear

C) 1200 done clear

D) 800 done clear

question_answer 58) In a plant species, flower colour yellow is dominant over white, and fruit shape round is dominant over elongated. Crossing was performed between two pure lines - one having yellow-flower and round fruit, and another with white-flower and elongated-fruit. About 20 plants survived in \[{{F}_{1}}\] progeny. Plants of \[{{F}_{1}}\] were allowed to self fertilize, and about 960 plants survived in \[{{F}_{2}}\]. If the traits follow Mendelian inheritance, the number of plants would have yellow flower and round fruit in \[{{F}_{1}}\] and \[{{F}_{2}}\] are respectively

A) 20, 960 done clear

B) 20, 540 done clear

C) 10, 180 done clear

D) 10, 60 done clear

question_answer 59) Two plants one with black flower and other with white coloured flower were crossed in an experiment. In the next generation grey coloured flowers were obtained. The reason for the result is

A) incomplete dominance done clear

B) pseudodominance done clear

C) codominance done clear

D) None of these done clear

question_answer 60) Genes which code for a pair of contrasting characters are called

A) factors done clear

B) traits done clear

C) alleles done clear

D) gametes done clear

question_answer 61) First husband of Asha had ABO blood type A and their child had type O. She remarried and her second husband had ABO blood type B and their child had type AB. What is the ABO genotype of Asha and also name her blood type?

A) ii; Blood type O done clear

B) \[{{I}^{B}}\,\,i\] ; Blood type B done clear

C) \[{{I}^{A}}{{I}^{B}}\]; Blood type AB done clear

D) \[{{I}^{A}}\,\,i\] ; Blood type A done clear

question_answer 62) During incomplete dominance, \[{{F}_{2}}\] generation will have

A) 3 : 1 genotypic ratio done clear

B) 3 : 1 phenotypic ratio done clear

C) 1 : 2 : 1 genotypic ratio done clear

D) 2 : 2 : 1 phenotypic ratio done clear

question_answer 63) Which of the following cross will give recessive progeny in \[{{F}_{1}}\] generation?

A) \[TT\,\,\,\,\times \,\,\,\,\,tt\] done clear

B) \[Tt\,\,\,\,\,\times \,\,\,\,TT\] done clear

C) \[tt\,\,\,\,\,\times \,\,\,\,\,tt\] done clear

D) \[TT\,\,\,\,\,\times \,\,\,\,\,\,TT\] done clear

question_answer 64) In a dihybrid cross between two heterozygotes \[AaBb\,\,\times \,\,Aa\,\,Bb\], if we get 3 : 1 ratio among the offsprings, the reason for this may be

A) polygenes done clear

B) linked genes done clear

C) pleiotropic genes done clear

D) hypostatic genes done clear

question_answer 65) What result Mendel would have got, had he self-pollinated a tall \[{{F}_{2}}\] plant?

A) TT and Tt done clear

B) All Tt done clear

C) All TT done clear

D) All tt done clear

question_answer 66) Test cross is a cross between

A) Hybrid \[\times \] dominant parent done clear

B) Hybrid \[\times \] recessive parent done clear

C) Hybrid \[\times \] hybrid parent done clear

D) Two distantly related species done clear

question_answer 67) Colchicine interferes with

A) Chromosome replication done clear

B) Organisation of spindle done clear

C) Chromosome condensation done clear

D) Incorporation of nitrogen base done clear

question_answer 68) Webbed neck is a characteristic of

A) XXY done clear

B) XY done clear

C) XXY done clear

D) XO done clear

question_answer 69) Daughter of a colour-blind father and normal mother marries a colour-blind person. Colour-blindness in the family shall be

A) 50% sons and 50% daughters done clear

B) All sons and daughters done clear

C) All daughters done clear

D) All sons done clear

What are depicted in the following figure of chromosome?

A) Dependent assortment of chromosomes done clear

B) Independent assortment of Chromatin done clear

C) Independent assortment of chromosomes done clear

D) Dependent assortment of Chromatin done clear

question_answer 71) Which one of the following statements is correct?

A) Down's syndrome occurs mostly in the children of very young mothers done clear

B) A person suffering from Down's syndrome has 47 chromosomes done clear

C) Down's syndrome is very common and occurs once is every 50 births done clear

D) Down's syndrome is caused when a sperm with an extra X chromosome fuses with a normal egg done clear

question_answer 72) Recessive characters are expressed when present:

A) Only when they are present on X chromosome of male done clear

B) Only when they are present on X chromosomes of female done clear

C) On any of autosome done clear

D) On any one chromosome done clear

question_answer 73) "Hypertrichosis" hairy ears are a sex-linked character associated with the

A) X chromosome done clear

B) XX chromosome done clear

C) XY chromosome done clear

D) Y chromosome done clear

question_answer 74) If this type of chromosome combination is found in man, we call this the "Klinefelter's syndrome"

A) One "X" chromosome and two "Y" chromosomes (XYY) done clear

B) Three "X" chromosomes (XXX) done clear

C) Three "Y" chromosomes (YYY) done clear

D) Two "X" chromosomes and one "Y" chromosome (XXY) done clear

question_answer 75) Mongoloid syndrome or Mongolian Idiocy is due to

A) 21 pairs normal, 22 and 23 extra chromosomes done clear

B) 22 pairs are normal, one chromosome has trisomy done clear

C) 24 pairs normal and one extra chromosome done clear

D) 22 pairs of normal chromosomes with one X chromosome done clear

question_answer 76) The exchange of generic material between chromatids of paired homologous chromosomes during first meiotic division is called

A) Transformation done clear

B) Chiasmata done clear

C) Crossing over done clear

D) Synapsis done clear

question_answer 77) Sex factor in bacteria

A) Chromosomal replicon done clear

B) F-Factor done clear

C) RNA - Fimbrae done clear

D) Sex-pilus done clear

question_answer 78) A person with 47 chromosomes due to an additional Y chromosome suffers from a condition called

A) Down's syndrome done clear

B) Super male done clear

C) Turner's syndrome done clear

D) Klinefelter's syndrome done clear

question_answer 79) For evolutionary success, a mutation must occur in

A) Germplasm DNA done clear

B) Somatic RNA done clear

C) Germplasm RNA done clear

D) Somatic DNA done clear

question_answer 80) Sometimes chromosome number increase or decrease due to:

A) Non-disjunction of chromosome done clear

B) Genetic repetition done clear

C) Mutation done clear

D) All of these done clear

The pedigree chart given below shows a particular trait which is absent in parents but present in the next generation irrespective of sexes. Draw your conclusion on the basis of the pedigree.

A) Allosome linked and recessive in nature done clear

B) Autosome linked and dominent in nature done clear

C) Allosome linked and dominent in nature done clear

D) Autosome linked and recessive in nature done clear

question_answer 82) Mutations are mainly responsible for controlling :

A) Increasing population rate done clear

B) Maintaining genetic continuity done clear

C) Variation in organisms done clear

D) Extinction of organisms done clear

question_answer 83) A woman with two genes, one for haemophilia and a gene for colour blindness on one of the 'X' chromosomes marries a normal man. Progeny will be : 

A) All sons and daughters haemophilic and colour-blind done clear

B) Haemophilic and colour-blind daughters done clear

C) 50% haemophilic colour-blind sons and 50% normal sons done clear

D) 50% haemophilic daughters and 50% colour-blind daughters done clear

question_answer 84) In Down's syndrome, karyotyping has shown that the disorder is associated with trisomy of chromosome number 21 usually due to

A) Addition of extra chromosome during mitosis of the zygote done clear

B) Non-disjunction during egg-cell formation done clear

C) Non-disjunction during sperm-cell formation done clear

D) Non-disjunction during formation of egg cells and sperm-cells done clear

question_answer 85) Mental retardation in man associated with sex chromosomal abnormality is usually due to :

A) Reduction in X complement done clear

B) Increase in X complement done clear

C) Moderate increase in Y complement done clear

D) Large increase in Y complement done clear

question_answer 86) Albinism is known to be due to an autosomal recessive mutation. The first child of a couple with normal skin pigmentation was an albino. What is the probability that their second child will also be an albino?

question_answer 87) One of the chief factors responsible for clotting of blood is present on :

A) X Chromosome of male only done clear

B) X Chromosome of female only done clear

C) X Chromosome of both male and female done clear

D) Autosomes only done clear

What is shown in the following figure of pedigrees?

A) Autosomal recessive trait like myotonic dystrophy done clear

B) Allosomal dominant trait like myotonic dystrophy done clear

C) Autosomal dominant trait like myotonic dystrophy done clear

D) Autosomal dominant trait like sickle - cell anaemia done clear

question_answer 89) A colour-blind daughter is born when :

A) Father is colour-blind, mother is normal done clear

B) Mother is colour-blind, father is normal done clear

C) Mother is carrier, father is normal done clear

D) Mother is carrier, father is colour-blind done clear

question_answer 90) In Down's syndrome (Mongolism) each cell has how many chromosomes:

A) 21st pair having one less done clear

B) 23rd pair with one less done clear

C) 45 chromosomes done clear

D) 47 chromosomes done clear

question_answer 91) Where are Barr bodies found?

A) Sperms of a man done clear

B) Ova of a woman done clear

C) Body cells (somatic) of man done clear

D) Body cells (somatic) of woman done clear

question_answer 92) The hereditary material present in the bacterium Escherichia coli is :

A) Single stranded DNA       done clear

B) Single stranded RNA done clear

C) Double stranded DNA done clear

D) Double stranded RNA done clear

question_answer 93) Extranuclear genes occur in which of the following:

A) Mitochondria and cytoplasm done clear

B) Ribosomes and cytoplasm done clear

C) ER and cytoplasm done clear

D) Cytoplasm and Lysosomes done clear

question_answer 94) Mutations generally occur in which of the following genes:

A) Dominant genes done clear

B) Recessive genes done clear

C) Lethal genes done clear

D) Mendel's genes done clear

question_answer 95) Significance of the telomere is that it :

A) Seals the chromosome done clear

B) Stretches the spindle fibres done clear

C) Synthesises proteins done clear

question_answer 96) Plasmids are useful in genetic engineering because they :

A) Replicate independently done clear

B) Carry useful genes done clear

C) Are common in eukaryotes done clear

D) Can be extracted from viruses done clear

question_answer 97) Strength of linkage is inversely proportional to distance between the :

A) Chromomeres done clear

B) Genes done clear

C) Telomeres done clear

D) Chromatids done clear

question_answer 98) If a group of genes are getting deleted and undergoing some change it is due to :

A) Gene mutation done clear

B) Aneuploidy done clear

C) Chromosomal mutation done clear

D) Gene modification done clear

question_answer 99) XX male and XY female are very rare in humans. They are due to :

A) Genes of Y-chromosome are on X chromosome done clear

B) Crossing over between X and Y done clear

C) Non-disjunction of chromosomes done clear

D) All of the above done clear

question_answer 100) Which of the following occurs more than one and less than five in chromosome?

A) Chromomere done clear

B) Chromatid done clear

C) Centromere done clear

D) Secondary constriction done clear

question_answer 101) Change in sequence of nucleotide in DNA plant is:

A) Mutation done clear

B) Isolation done clear

C) Polyploidy done clear

D) Sexual reproduction done clear

question_answer 102) The segment of DNA which participates in crossing over is known as :

A) Muton done clear

B) Cistron done clear

C) Recon done clear

D) Replicon done clear

question_answer 103) Trisomy is :

A) One chromosome less than 2n. done clear

B) One chromosome more than 2n done clear

C) A hybrid obtained by crossing diploid and tetraploid done clear

D) Three chromosomes more than 2n done clear

question_answer 104) Kappa particles in Paramecium are indicating:

A) Nuclear inheritance done clear

B) Cytoplasmic inheritance done clear

C) Nucleo-cytoplasmic inheritance done clear

D) Mutation done clear

question_answer 105) Major role of colchicine in the eukaryotic cell is in :

A) Reducing number of chiasmata done clear

B) Causing endoduplication done clear

C) Dividing the nucleus done clear

D) Formation of polytene chromosome done clear

question_answer 106) The genes present exclusively on the X-chromosome in humans is concerned with :

A) Baldness and trichosis done clear

B) Night-blindness done clear

C) Facial hair and moustaches in males done clear

D) Red-green colour blindness done clear

question_answer 107) Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of offsprings produced by an affected mother and normal father would be affected by this disorder?

A) 75% done clear

C) 25% done clear

question_answer 108) Linkage map of X-chromosome of fruit fly has 66 units, with yellow body gene (y) at one end and bobbed hair [b] gene at the other end. The recombination frequency between these two genes (y and b) should be :

A) > 75% done clear

B) < 50% done clear

C) 100% done clear

D) 66% done clear

question_answer 109) Genetic map of a eukaryotic cell is one that :

A) Shows the stages during cell division done clear

B) Establishes various stages in gene evolution done clear

C) Establishes sites of genes on a chromosome done clear

D) Shows the distribution of various species in a region done clear

question_answer 110) Genes for cytoplasmic male sterility in plants are generally located in :

A) Cytosol done clear

B) Nuclear genome done clear

C) Chloroplast genome done clear

D) Mitochondrial genome done clear

question_answer 111) When a diploid female plant (2n) is crossed with a tetraploid male plant (4n), then ploidy of endosperm cells in the resulting seed is :

A) Triploidy done clear

B) Diploidy done clear

C) Pentaploidy done clear

D) Tetraploidy done clear

question_answer 112) After the mutation at a genetic locus, the character of an organism changes due to change in :

A) DNA replication done clear

B) Protein structure done clear

C) RNA transcription pattern done clear

D) Protein synthesis pattern done clear

question_answer 113) One of the parents of a cross has a mutation in its mitochondria segregation of F2 progenies, mutaticz is found in :

A) All the progenies done clear

C) One-third of the progenies done clear

D) Fifty percent of progenies done clear

question_answer 114) Lack of independent assortment of genes A and B in fruit fly Drosophila is due to :

A) Repulsion done clear

B) Linkage done clear

D) Recombination done clear

Given below is the representation of a kind of chromosomal mutation. What is kind of mutation represented

A) Deletion done clear

B) Duplication done clear

C) Inversion done clear

D) Translocation done clear

question_answer 116) Haemophilia is more commonly seen in human males than in human females because :

A) A greater proportion of girls die in infancy done clear

B) This disease is due to an Y linked recessive mutation done clear

C) This disease is due to an X linked recessive mutant done clear

D) This disease is due to an X linked dominant mutation done clear

question_answer 117) In Drosophila, gene for white eye mutation is also responsible for depigmentation of body parts. Thus gene that controls several phenotypes is called :

A) Oncogene done clear

B) Epistatic gene done clear

C) Hypostatic gene done clear

D) Pleiotropic gene done clear

question_answer 118) Phenylketonuria is the genetic disorder of :

A) Trisomic condition done clear

B) Monosomic condition done clear

C) Autosomal dominant gene done clear

D) Autosomal recessive gene done clear

question_answer 119) Haemophilia is a condition, where there is :

A) No production of haemoglobin in the blood done clear

B) No production of melanin in the skin done clear

C) A failure of clotting mechanism of blood done clear

D) A delay in clotting of blood done clear

question_answer 120) When the chromosome number of a given organism has one additional chromosome in one of the homologous pairs, the condition is known as

A) Trisomy done clear

B) Monosomy done clear

D) Nullisomy done clear

question_answer 121) In a skip generation inheritance of colour-blindness trait from a colour-blind man is passed on to :

A) Daughter done clear

B) Son done clear

C) Grand daughter done clear

D) Grand son done clear

question_answer 122) A medico-legal case of accidental interchange between two babies in a hospital, the baby of the blood group 'A' could not be rightly given to couple with :

A) Husband of 'O' group and wife of 'AB' group done clear

B) Husband of 'A' group and wife of 'B' group done clear

C) Husband of 'B' group and wife of 'O' group done clear

D) Husband of 'AB' group and wife of 'A' group done clear

question_answer 123) Genes present is cytoplasm of eukaryotic cells are found in :

A) Mitochondria and inherited via egg cytoplasm done clear

B) Lysosomes and peroxisomes done clear

C) Golgi bodies and smooth endoplasmic reticulum done clear

D) Plastids and inherited via male gamete done clear

question_answer 124) Action of ultraviolet rays on DNA is :

A) Induction of thymidine done clear

B) Deletion of base pair done clear

C) Addition of base pair done clear

D) Methylation of base pair done clear

question_answer 125) In Klinefelter's syndrome, the sex chromosome complement is :

A) 22A + XXY done clear

B) 22 A + XO done clear

C) 22 A + XY done clear

D) 22 A + XX done clear

question_answer 126) The recessive genes located on X-chromosome in humans are always :

A) Lethal in male and female done clear

B) Sub-lethal in male and female done clear

C) Expressed in males done clear

D) Expressed in females done clear

question_answer 127) After a mutation at a genetic locus, the character of an organism changes due to the change in :

A) Protein structure done clear

B) DNA replication done clear

C) Enzyme pattern done clear

D) RNA transcription pattern done clear

question_answer 128) A man and a woman, who do not show any apparent signs of certain inherited disease, have seven children (2 daughters and 5 sons). Three of the sons suffer from the given disease but none of the daughters are affected. Which of the following mode of inheritance, do you suggest for the disease?

A) Autosomal dominant done clear

B) Sex-linked dominant done clear

C) Sex-limited recessive done clear

D) Sex-linked recessive done clear

question_answer 129) A woman with normal vision, but whose father was colour-blind, marries a colour-blind man. Suppose that the fourth child of this couple was a boy. This boy :

A) Must have normal colour vision done clear

B) Will be partially colour-blind since he is heterozygous for the colour-blind mutant allele done clear

C) Must be colour-blind done clear

D) May be colour-blind or may be of normal vision done clear

question_answer 130) Haemophilia is more commonly seen in human males than in human females because :

A) This disease is due to an X-linked dominant mutation done clear

B) A greater proportion of girls die in infancy done clear

C) This disease is due to X-linked recessive mutation done clear

D) This disease is due to Y-linked recessive mutation done clear

question_answer 131) A woman with 47 chromosomes due to three copies of chromosome 21 is characterized by:

A) Down syndrome done clear

B) Triploidy done clear

C) Turner syndrome done clear

D) Super femaleness done clear

question_answer 132) Barr body of a mammal represents :

A) All heterochromatin in female cells done clear

B) All heterochromatin in male and female cells done clear

C) The Y chromosome in the somatic cells of male done clear

D) One of the two X-chromosomes in somatic cells of female done clear

question_answer 133) Genetic counsellors can identify heterozygous individuals by :

A) Height of an individuals done clear

B) Colour of an individuals done clear

C) Screening procedures done clear

D) Weight of an individual done clear

question_answer 134) A marriage between normal visioned man and colour-blind woman will produce, which of the following type of offspring?

A) Normal sons and carrier daughters done clear

B) Colour-blind sons and carrier daughters done clear

C) Colour-blind sons and 50% carrier daughters done clear

D) 50% colour-blind sons and 50% carrier daughters done clear

question_answer 135) Linkage group in Escherichia coli is/are :

A) 4 done clear

C) 1 done clear

question_answer 136) Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder?

A) 50% done clear

question_answer 137) Grain colour in wheat is determined by three pairs of polygenes. Following the cross AABBCC (dark colour) \[\times \] aabbcc (light colour), in \[{{F}_{2}}\] generation what proportion of the progeny is likely to resemble either parent?

A) Half done clear

B) Less than 5 percent done clear

C) One third done clear

question_answer 138) Complete linkage is observed in :

A) Male Drosophila sp. done clear

B) Female Drosophila sp. done clear

C) Female silkworm done clear

D) Female rhesus monkey done clear

question_answer 139) Mutations that arise suddenly in nature are called :

A) Chromosomal mutations done clear

B) Induced mutations done clear

C) Gene mutations done clear

D) Spontaneous mutations done clear

question_answer 140) Occurrence of cell containing multiples of 2n genomes in diploid organisms is known as :

A) Aneuploidy done clear

B) Alloploidy done clear

C) Amphiploidy done clear

D) Endopolyploidy done clear

question_answer 141) Skin colour in man is determined by three pairs of polygenes. Following the cross AABBCC (dark colour) \[\times \] aabbcc (light colour), in \[{{F}_{2}}\] generation what proportion of the progeny is likely to resemble either parent?

B) 3% done clear

question_answer 142) Which of the following pair of features is a good example of polygenic inheritance?

A) Human height and skin colour done clear

B) ABO blood group in humans and flower colour of Mirabilis jalapa done clear

C) Hair pigment of mouse and tongue rolling in humans done clear

D) Human eye colour and sickle cell anaemia done clear

question_answer 143) The gene which controls many characters is called :

A) Codominant gene done clear

B) Polygene done clear

C) Pleiotropic gene done clear

D) Multiple gene done clear

question_answer 144) Sickle cell anaemia is :

A) Autosomal dominant inheritance done clear

B) X-linked recessive inheritance done clear

C) Autosomal recessive inheritance done clear

D) X-linked dominant inheritance done clear

question_answer 145) Polyploidy can be produced artificially by :

A) Colchicine done clear

B) Inbreeding done clear

C) Line breeding done clear

D) Self-pollination done clear

question_answer 146) Karyotype is :

A) Chromosome complement which is specific for each species of living organism done clear

B) All organisms possessing same type of chromosomes done clear

C) Division of nucleus done clear

D) One of the above done clear

question_answer 147) Identify the wrong statements:

A) In male grasshoppers 50 % of the sperms have no sex chromosome done clear

B) Usually female birds produce two types of gametes based on sex chromosomes done clear

C) The human males have one of their sex chromosomes much shorter than the other done clear

D) In domesticated fowls the sex of the progeny depends on the type of sperm that fertilizes the egg done clear

question_answer 148) Gynaecomastia is a common feature seen in:

B) Turner's syndrome done clear

C) PKU done clear

question_answer 149) The graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross is called :

A) Pedigree analysis done clear

B) Karyotype done clear

C) Punnett square done clear

D) Chromosome map done clear

question_answer 150) Chromosome is made up of :

A) DNA + pectin done clear

B) RNA + DNA done clear

C) DNA + histone done clear

D) Only histone done clear

What is shown in the following figure of human pedigrees?

A) Autosomal dominant trait like Sickle - cell anaemia done clear

B) Allosomal recessive trait like Sickle - cell anaemia done clear

C) Autosomal recessive trait like colour blindness done clear

D) Autosomal recessive trait like Sickle - cell anaemia done clear

question_answer 152) In honeybee haploid stage develop into

A) Male caste done clear

B) Female caste done clear

C) Neutral caste done clear

question_answer 153) The number of linkage group(s) present in man is :

A) One done clear

B) Two done clear

C) Twenty-three done clear

D) Seven done clear

question_answer 154) The major cause of evolution of genes and protein is :

A) Point mutation done clear

B) Chromosomal aberration done clear

C) Sexual reproduction done clear

D) Gene duplication and divergence done clear

question_answer 155) Due to nondisjunction of chromosomes during spermatogenesis, sperms carry both sex chromosomes (22A + XY) and some sperms do not carry any sex chromosome (22A + X). If these sperms fertilize normal eggs (22A + X), what types of genetic disorders appear among the offsprings?

A) Turner's syndrome and Klinefelter's syndrome done clear

B) Down's syndrome and Klinefelter's syndroos done clear

C) Down's syndrome and Turner's syndrome done clear

D) Down's syndrome and cri-du-chat syndrora done clear

question_answer 156) Which genetic disorder is caused due to the presence of an additional copy of X-chromosome (A Karyotype of 44, XXY)?

A) Klinefelter's syndrome done clear

B) Down's syndrome done clear

D) Edward's syndrome done clear

question_answer 157) Multiple phenotype is seen in:

A) dominance relationship done clear

B) paniculate inheritance done clear

C) monogenic inheritance done clear

D) polygenic inheritance done clear

question_answer 158) Cystic Fibrosis disease in human being is due to

A) chromosome 5 done clear

B) chromosome 6 done clear

C) chromosome 7 done clear

D) chromosome 8 done clear

question_answer 159) In XO type of sex determination

A) females produce two different types of gametes done clear

B) males produce two different types of gametes done clear

C) females produce gametes with Y chromosomes done clear

D) males produce single type of gametes done clear

question_answer 160) Who used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and mapped their position on the chromosome?

B) Correns done clear

C) Tschermark done clear

D) Alfred Sturtevant done clear

question_answer 161) Sickle cell anaemia is caused by the substitution of

A) valine by glutamic acid at sixth position of alpha chain of haemoglobin. done clear

B) valine by glutamic acid at sixth position of beta chain of haemoglobin. done clear

C) glutamic acid by valine at sixth position of alpha chain of haemoglobin. done clear

D) glutamic acid by valine at sixth position of beta chain of haemoglobin done clear

question_answer 162) Which following pair of diseases is caused by two genes located on human X-Chromosome?

A) Colour blindness and phenylketonuria. done clear

B) Colour blindness and haemophilia. done clear

C) Colour blindness and albinism. done clear

D) Colour blindness and hypertrichosis. done clear

question_answer 163) XX-XO type sex determination is recorded in

A) Grasshopper done clear

B) Drosophila done clear

C) Frog done clear

D) Earthworm done clear

question_answer 164) In XO types of sex determination

B) Males produce two different types of gametes done clear

question_answer 165) The behaviour of the chromosomes was parallel to the behaviour of genes during meiosis was noted by

A) Correns done clear

B) Tschermark done clear

C) Sutton and Boveri done clear

D) de Vries done clear

question_answer 166) Genes with multiple phenotypic effects are known as

A) hypostatic genes done clear

B) duplicate genes done clear

D) complementary genes done clear

question_answer 167) In case of incomplete linkage, the parental combinations obtained in \[{{F}_{2}}\], generation are

B) more than 50% done clear

D) less than 50% done clear

question_answer 168) Loss or gain of one more complete set of chromosomes along with the diploid complement is known as

A) aneuploidy done clear

B) euploidy done clear

C) reverse tandem duplication done clear

D) substitution done clear

question_answer 169) The traits which are expressed in only a particular sex through their genes occurs in the opposite sex too are known as

A) sex linked trait done clear

B) sex influence trait done clear

C) sex limited traits done clear

D) sex affected traits done clear

question_answer 170) Heterogamety is the term where an individual produces two types of gametes. The most appropriate answer is

A) Male Drosophila fly done clear

B) Female Drosophila fly done clear

C) Female bird done clear

D) Both [a] and [c] done clear

question_answer 171) In our society women are blamed for producing female children. Choose the correct answer for the sex-determination in humans.

A) Due to some defect like aspermia in man done clear

B) Due to the genetic make up of the particular sperm which fertilizes the egg done clear

C) Due to the genetic make up of the egg done clear

D) Due to some defect in the women. done clear

question_answer 172) Genetic variation in a population arises due to

A) recombination only done clear

B) mutation as well as recombination done clear

C) reproductive isolation and selection done clear

D) mutations only done clear

question_answer 173) Which one is the incorrect statement with regard to the importance of pedigree analysis?

A) It confirms that DNA is the carrier genetic information              done clear

B) It helps to understand whether the trait in question is dominant or recessive. done clear

C) It confirms that the trait is linked to one of the autosomes. done clear

D) It helps to trace the inheritance of a specific trait. done clear

question_answer 174) A colour-blind man marries the daughter of another colour-blind man whose wife has a normal genotype for colour vision. In their progeny

A) all the children would be colour-blind done clear

B) all their sons are colour-blind done clear

C) none of the daughters would be colour-blind done clear

D) half of their sons and half of their daughters would be colour-blind. done clear

question_answer 175) Klinefelter's syndrome in human is an example of

A) Auto polyploidy done clear

B) Allopolyploidy done clear

C) Diploidy done clear

D) Aneuploidy done clear

question_answer 176) A person affected with phenylketonuria, lacks an enzyme that converts the amino acid phenylalanininto

A) valine done clear

B) proline done clear

C) histidine done clear

D) tyrosine done clear

question_answer 177) In sickle cell anemia, the sequence of amino acids from the first to the seventh position of the p-chain of haemoglobin S(HbS) is

A) His, Leu, Thr, Pro, Glu, Val, Val done clear

B) Val, His, Leu, Thr, Pro, Glu, Glu done clear

C) Thr, His, Pro, Val, Pro, Val, Glu done clear

D) Val, His, Leu, Thr, Pro, Val, Glu done clear

Statement-A: For a particular character in an individual, each gamete gets only one allele.

Statement-B: Chromatids of a chromosome split (separate) and move towards opposite poles during anaphase of mitosis.

A) Statement A is correct and statement B is wrong. done clear

B) Both the statements are correct and B is the reason for A. done clear

C) Statement B is correct and statement A is wrong. done clear

D) Both the statements are correct and B is not the reason for A. done clear

question_answer 179) Sickle cell anaemia is caused due to the substitution of

A) valine at the 6th position of beta globin chain by glutamine done clear

B) valine at the 6th position of alpha globin chain by glutamic acid done clear

C) glycine at the 6th position of alpha globin chain by glutamic acid done clear

D) glutamic acid at the 6th position of beta globin chain by valine done clear

question_answer 180) Anish is having colour blindness and married to Sheela, who is not colour-blind. What is the chance that their son will have the disease?

D) 0% done clear

question_answer 181) The frequency of crossing over occurring between two genes located on the same chromosome depends on

A) length of the chromosome done clear

B) position of the centromere done clear

C) activities of two genes done clear

D) distance between two genes done clear

question_answer 182) The enzyme involved in the crossing over between two homologous chromosomes is

A) nuclease done clear

B) RNA polymerase done clear

C) recombinase done clear

D) DNA polymerase done clear

question_answer 183) A couple, both carriers for the gene sickle cell anaemia planning to get married, wants to know the chances of having anaemic progeny?

B) 75% done clear

D) 25% done clear

question_answer 184) The total number of types of gametes produced in across between a negro and albino parent is

A) 64 done clear

B) 16 done clear

C) 08 done clear

D) 04 done clear

question_answer 185) Which of the following is correct match?

I		II		III
Thalassemia	[A]	XO	(i)	Flat nose, simian crease

I		II		III
Down's syndrome	[B]	42 AA + XY	(ii)	Webbing of neck

I		II		III	I
	Turner's syndrome	[C]	44 AA + XXX	(iii)	Anaemia, jaundice

I		II		III
Klinefelter's syndrome	[D]	44 AA + XXY	(iv)	Tall, thin, eunuchoid

question_answer 186) Sex determination by chromosomal difference in man and Drosophila is by mechanism called

A) XX-XY                    done clear

B) XX-XO done clear

C) ZZ-ZW done clear

D) Both [a] and [b] done clear

question_answer 187) Which of the following set of syndromes show 47 chromosomes in their genetic make up?

A) Down's syndrome, Patau's syndrome, Edward's syndrome done clear

B) Turner's syndrome, Edward's syndrome, Klinefelter's syndrome done clear

C) Klinefelter's syndrome. Turner's syndrome, Edward's syndrome done clear

D) All the above done clear

question_answer 188) In order to lessen the suffering of phenylketonurics their diet should have

A) no phenylalanine and no tyrosine done clear

B) low phenylalanine and normal requirement of tyrosine done clear

C) normal recommended amount of phenylalanine done clear

D) normal recommended amount of both phenylalanine and tyrosine done clear

question_answer 189) Drosophila flies with XXY genotype are females, but human beings with such genotype are abnormal males. It shows that :

A) Y-chromosome is essential for sex determination in Drosophila done clear

B) Y-chromosome in female determining in Drosophila done clear

C) Y-chromosome is male determining in human beings done clear

D) Y-chromosome has no role in sex determination either in Drosophila or in human beings done clear

Linkage groups :

1. Have genes, which were linked together in a single chromosome

2. Show independent assortment

3. Do not show independent assortment

4. In prokaryotes are more than one

question_answer 191) Which of the following statements about colour blindness is correct?

A) 2% men are red colour blind, 6% are green colour blind done clear

B) 6% men are red colour blind, 2% are green colour blind done clear

C) 10% men are red colour blind, 5% are green colour blind done clear

D) 5% men are red colour blind, 10% are green colour blind done clear

question_answer 192) Choose the wrong statement.

A) In grasshoppers, besides autosomes males have only one X-chromosome, whereas females have a pair of X-chromosomes. done clear

B) In XY type of sex determination, both males and females have same number of chromosomes. done clear

C) In Drosophila, males have one X and one Y chromosome, whereas females have a pair of X- chromosomes besides autosomes done clear

D) In insects with XO type of sex determination, all sperms bear X-chromosome besides autosomes done clear

question_answer 193) Which one of the following is an example of poly genie inheritance?

A) Flower colour in Mirabilis jalapa done clear

B) Production of male honey bee done clear

C) Pod shape in garden pea done clear

D) Skin colour in humans done clear

question_answer 194) Identify a Mendelian disorder from the following :

C) Phenylketonuria done clear

D) Kline feller's syndrome done clear

question_answer 195) A man, whose father is colour blind, marries a lady who is daughter of a colour-blind man. Their off springs will be

A) all normal done clear

B) all colour blinds done clear

C) all sons colour blind done clear

D) some sons colour blind and some normal done clear

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Unit 4: Principles of inheritance and variation

Introduction to mendelian genetics.

• Introduction to heredity (Opens a modal)
• An Introduction to Mendelian Genetics (Opens a modal)
• Why Mendel chose peas (Opens a modal)
• Mendel and his peas (Opens a modal)
• Introduction to heredity review (Opens a modal)
• Introduction to heredity Get 3 of 4 questions to level up!

Monohybrid cross - Mendel's laws of dominance and segregation

• Mendel's experiment (monohybrid cross) (Opens a modal)
• Dominance & segregation laws (Opens a modal)
• The law of segregation (Opens a modal)
• Mendel's Experiments Get 3 of 4 questions to level up!
• Monohybrid punnett squares Get 3 of 4 questions to level up!

Dihybrid cross - law of independent assortment

• Independent assortment (dihybrid cross) (Opens a modal)
• The law of independent assortment (Opens a modal)
• Punnett squares and probability Get 3 of 4 questions to level up!
• Dihybrid punnett squares Get 3 of 4 questions to level up!

Non-Mendelian genetics

• Variations on Mendel's laws (overview) (Opens a modal)
• Co-dominance and incomplete dominance (Opens a modal)
• Multiple alleles, incomplete dominance, and codominance (Opens a modal)
• Worked example: Punnett squares (Opens a modal)
• Polygenic inheritance and environmental effects (Opens a modal)
• Non-Mendelian inheritance review (Opens a modal)
• Non-Mendelian inheritance Get 3 of 4 questions to level up!

Chromosomal theory of inheritance

• Boveri-Sutton chromosome theory (Opens a modal)
• Thomas Hunt Morgan and fruit flies (Opens a modal)
• The chromosomal basis of inheritance (Opens a modal)
• Chromosomes, linkage and recombination - Part 1 (Opens a modal)
• Chromosomes, linkage and recombination - Part 2 (Opens a modal)
• Chromosomes, linkage and recombination - Part 3 (Opens a modal)
• Gene Mapping (Opens a modal)
• Genes and chromosomes Get 3 of 4 questions to level up!
• Chromosome theory of inheritance Get 3 of 4 questions to level up!
• Chromosomes, linkage and recombination Get 3 of 4 questions to level up!
• Recombination frequency and gene mapping Get 3 of 4 questions to level up!

Sex determination, linkage, and chromosomal disorders

• Sex determination (Opens a modal)
• Sex Determination in Birds (Opens a modal)
• Sex Determination in Honey Bees (Opens a modal)
• X-linked inheritance (Opens a modal)
• Worked example: Punnett square for sex-linked recessive trait (Opens a modal)
• Aneuploidy & chromosomal rearrangements (Opens a modal)
• X-inactivation (Opens a modal)
• Sex Determination in humans Get 3 of 4 questions to level up!
• Sex linkage Get 3 of 4 questions to level up!
• Sex-linked traits Get 3 of 4 questions to level up!
• X-inactivation and aneuploidy Get 3 of 4 questions to level up!

Mendelian disorders and pedigree analysis

• An introduction to genetic mutations (Opens a modal)
• Pedigrees (Opens a modal)
• Pedigree for determining probability of exhibiting sex linked recessive trait (Opens a modal)
• Pedigrees review (Opens a modal)
• Pedigrees Get 3 of 4 questions to level up!

Principles of Inheritance and Variation Class 12th: MCQ & Extra Questions

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looking to master the principles of inheritance and variation? Look no further! In this comprehensive article, we have compiled 100 questions with detailed answers, including multiple-choice questions (MCQs), to help you gain a thorough understanding of this important topic. From Mendelian inheritance to genetic mutations and DNA recombination, these questions cover a wide range of concepts and scenarios related to inheritance and variation.

Whether you're a student preparing for exams or a curious learner wanting to deepen your knowledge, this article is your one-stop resource. Each question is designed to challenge your understanding and test your knowledge of the principles at hand. With clear, concise answers provided, you can confidently check your comprehension and clarify any lingering doubts. By engaging with these questions, you'll develop a solid foundation in the principles of inheritance and variation. Ready to embark on this educational journey? Let's dive in and expand our understanding of the fascinating world of genetics.

The study of Principles of Inheritance and Variation is an integral part of Class 12 Biology, specifically covered in Chapter 4. This chapter delves into the complexities of how traits are passed down from one generation to another and explores the concept of genetic variation within populations. Students, particularly those gearing up for competitive exams like NEET, will find that focusing on Principles of Inheritance and Variation Class 12 important questions can help reinforce key concepts. These important questions are often framed around fundamental topics like Mendelian genetics, mutations, and chromosomal disorders.

When preparing for Class 12 board exams or NEET, a question bank can be highly beneficial. Various educational platforms and books offer Principles of Inheritance and Variation question bank, featuring a wide range of questions, including multiple-choice questions (MCQs). To make the most of your preparation time, consider downloading Principles of Inheritance and Variation MCQ PDF, which typically includes answers and explanations. These MCQs are not just pivotal for board exams but are also frequently seen in NEET, making them doubly valuable. You'll find that many Principles of Inheritance and Variation Class 12 MCQ NEET questions have also appeared as previous year questions (PYQ), offering a good understanding of the exam pattern.

For those looking for a focused revision strategy, Principles of Inheritance and Variation Class 12 notes for NEET can provide a quick yet comprehensive review of the chapter. These notes are designed to highlight the most important topics, often featuring case study questions and extra questions for further practice. If you're aiming to cover all bases, Principles of Inheritance and Variation worksheet can help solidify your understanding, featuring a range of questions from easy to complex. Moreover, these worksheets often come with answers, aiding in self-assessment.

Understanding the Principles of Inheritance and Variation is not just crucial for academic success but also offers real-world applications, such as in the fields of medicine and agriculture. Therefore, a thorough grasp of this chapter is essential. Whether you're working through Principles of Inheritance and Variation Class 12 NCERT questions or practicing from a dedicated MCQ PDF, the objective remains the same: mastering the key concepts to excel in both your board exams and competitive tests like NEET. And for that, tapping into a variety of resources, from notes PDF for board exams to important questions for NEET, can offer a well-rounded preparation strategy.

Mendelian Genetics: Understanding the Basics

Mendelian Genetics refers to the set of principles formulated by Gregor Mendel based on his pea plant experiments. These principles provide a fundamental understanding of how traits are inherited. Mendel's work laid the foundation for the field of genetics, explaining how traits pass from parents to offspring through genes. Understanding Mendelian genetics is crucial for grasping more complex topics in genetics and offers foundational knowledge for future studies.

Laws of Inheritance: Mendel's Experiments and Discoveries

Mendel proposed three laws of inheritance based on his experiments: the Law of Segregation, the Law of Independent Assortment, and the Law of Dominance. These laws explain how individual traits are inherited independently and describe the dominant and recessive nature of genes. Grasping Mendel's laws is vital for comprehending more complex genetic interactions.

Patterns of Inheritance: Monohybrid and Dihybrid Crosses

Monohybrid crosses involve one trait, whereas dihybrid crosses involve two traits. These types of crosses are essential for understanding how traits are inherited separately or together. Monohybrid crosses can illustrate the Law of Segregation, while dihybrid crosses can demonstrate the Law of Independent Assortment.

Exceptions to Mendelian Genetics: Incomplete Dominance, Codominance, and Multiple Alleles

While Mendel's principles apply broadly, some exceptions do exist. Examples include incomplete dominance, where neither allele is dominant, and codominance, where both alleles are equally dominant. Understanding these exceptions allows students to appreciate the complexity of genetic inheritance.

Linkage and Crossing Over: Understanding Genetic Linkage

Genes that are located close together on the same chromosome tend to be inherited together, known as genetic linkage. Crossing over during meiosis can, however, break this linkage, leading to new combinations of traits. This topic provides insights into the dynamics of gene combinations and inheritance patterns.

Chromosomal Abnormalities: Structural and Numerical Aberrations

Chromosomal abnormalities can occur in the structure or number of chromosomes and often result in genetic disorders. Understanding these abnormalities is essential for grasping the complexities of human genetics and for the study of medicine.

Sex Determination and Sex-Linked Inheritance

Sex determination deals with how the sex of an individual is established, often through chromosomes like X and Y. Sex-linked inheritance involves genes located on these sex chromosomes, and understanding this is crucial for studying genetic disorders specific to one gender.

Genetic Variation: Mutations and Genetic Disorders

Genetic variation arises due to mutations, which are changes in the DNA sequence. Some mutations result in genetic disorders that can be inherited. Learning about mutations allows for a deeper understanding of genetic diversity and disease.

Modern Concepts in Genetics: Polygenic Inheritance, Epistasis, and Pleiotropy

Modern genetics has expanded upon Mendel's work to include concepts like polygenic inheritance, where multiple genes affect a single trait. Epistasis involves the interaction between genes, and pleiotropy occurs when one gene influences multiple traits. These modern concepts provide a more complete understanding of the complexities of genetics.

Each of these topics adds a layer of understanding to the overarching subject of inheritance and variation, essential for Class 12 Biology and beyond.

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• Class 12 Biology Principles...

Class 12 Biology Principles of Inheritance and Variation Extra Questions

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Class 12 Biology Principles of Inheritance and Variation Extra Questions. myCBSEguide has just released Chapter Wise Question Answers for class 12 Biology.  There chapter wise Test papers with complete solutions are available for download in  myCBSEguide   website and mobile app. These Extra Questions with solution are prepared by our team of expert teachers who are teaching grade in CBSE schools for years. There are around 4-5 set of solved Biology Extra questions from each and every chapter. The students will not miss any concept in these Chapter wise question that are specially designed to tackle Board Exam. We have taken care of every single concept given in  CBSE Class 12 Biology   syllabus  and questions are framed as per the latest marking scheme and blue print issued by CBSE for Class 12.

CBSE Class 12 Biology Ch – 5 Test Papers

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Important Questions for Class 12 Biology Chapter 5

Ch-5 Principles of Inheritance and Variation

• Crossing of F1 and F2
• Crossing of F3 and F4
• Selfing of F2
• Selfing of F1
• Segment of chromosome
• Segments of mitochondria
• Segment of nucleus
• Segment of DNA
• Non-cross over percentage
• Recombination frequency of each gene locu
• Cross over percentage
• Number of mutant genes
• Purity of gametes
• Law of independent assortment
• Segregation
• Only recessive allele
• Only one of the alleles
• Only dominant allele
• The phenotypic and genotypic ratios in  F 2 F2  generation are same in a certain kind of inheritance. Name and organism in which it occurs and mention the kind of inheritance involved.
• A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
• A garden pea plant produced round green seeds. Another of the same species produced wrinkled yellow seeds. Identify the dominant traits.
• Kavita’s parents suffer from high blood pressure and are obess. Kavita is also worried about her health. Do you think kavita can inherit these characteristic from parent. Suggest two measures kavita can adopt to avoid high blood pressure and obesity.
• How is sex determined in human beings?
• Briefly mention the contribution of T.H. Morgan in genetics.
• How is a child affected if it has grown from the zygote formed by an XX-egg fertilized by a Y-carrying sperm? What do you call this abnormality?
• Is the trait recessive or dominant?
• Is the trait sex-linked or autosomal?
• Give the genotypes of the parents shown in generation I and their II child is shown in generation II and the first grandchild shown in generation III.
• Give all the possible genotype of the members 4, 5 and 6 in the pedigree chart.
• A blood test shows that the individual 14 is a carrier of haemophilia. The member numbered 15 has recently married the member numbered 14. What is the probability that their first child will be a haemophilic male?

A homozygous tall pea plant with green seeds is crossed with a dwarf pea plant with yellow seeds.

• What would be the phenotype and genotype of F 1  generation?
• Work out the phenotypic ratio of F 2  generation with the help of a Punnett square.
• Selfing of F1,  Explanation:  In monohybrid and dihybrid cross F2 generation is obtained by selfing of Fi hybrids as male and female.
• Segment of DNA,  Explanation:  Genes are segment of DNA present on chromosome. Large numbers of genes are located on single chromosome. A gene or genes determines the traits of the individual.
• Cross over percentage,  Explanation:  Map distance is tools to find the distance between two genes on a chromosome. The genes closer to each other shows less number of crossing over percentage.
• Law of independent assortment,  Explanation:  In dihybrid cross, two new kinds of plants with new trait are formed. This is possible only when all traits assort independently and recombine to form new combination.
• Only one of the alleles,  Explanation:  Each gametes carry single set of chromosomes. During gamete formation each pair of alleles separate from each other as reduction division occurs.
• It occurs in snapdragon / antirrhinum sp. (dog flower). The inheritance involved is incomplete dominance.
• 2 4 24  (16 gametes can be produced) types
• Round and yellow.
• 1) No, these are life style related diseases 2) Any two measures- changing in food habits, exercises, leading active life, meditation. Values • Awareness about health. • Understanding.
• A baby’s genetic sex is determined at the time of conception. When the baby is conceived, a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell, determining whether the baby will be genetically female (XX) or male (XY).
• Thomas Hunt Morgan put forth chromosome theory of linkage from this work on fruit fly (Drosophila melanogaster). He established the principle of linkage, discovered sex linkage and technique of chromosomal mapping. He wrote a book ‘Theory of Gene’ and was awarded Nobel Prize in 1933.
• The union of an abnormal XX egg and a normal Y sperm results in trisomy of sex (X) chromosome. This is a type of sex chromosomal abnormality where the individual has 47 chromosomes (44 + XXY) and the abnormality is called Klenifelter’s syndrome.
• Parents Mother -aa Father – Aa Third child – Aa First grandchild – Aa
• Members Genotypes 4X h X 4X h X 6 XY

Male		Female
		X	X
	X	X X	XX
	Y	X Y	XY

• Phenotypically all the plants of F 1   generation would be tall with green seeds. The genotype of all the would-be Tt Gg. i.e. hybrid tall plant with green seeds.

	T	t
	TG	tg
	Tg	tg

	TG	tg	Tg	tg
	TTGG	TtGG	TTGg	TtGg
	TtGG	ttGG	TtGg	ttGg
	TTGg	TtGg	TTgg	Ttgg
	ttGg	Ttgg	Ttgg	ttgg

Class 12 Biology Chapter Wise Test Paper

• Reproduction in Organisms
• Sexual Reproduction in Flowering Plants
• Human Reproduction
• Reproductive Health
• Principles of Inheritance and Variation
• Molecular Basis of Inheritance
• Human Health and Disease
• Strategies for Enhancement in Food Production
• Microbes in Human Welfare
• Biotechnology Principles and Processes
• Biotechnology and its Applications
• Organisms and Populations
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Case Based Questions Test: Principles of Inheritance & Variation - 2 - NEET MCQ

15 questions mcq test - case based questions test: principles of inheritance & variation - 2, direction: read the following text and answer the following questions on the basis of the same : sickle cell anaemia is a genetic disorder where the body produces an abnormal haemoglobin called haemoglobins. red blood cells are normally flexible and round, but when the haemoglobin is defective, blood cells take on a “sickle” or crescent shape. sickle cell anaemia is caused by mutations in a gene called hbb. it is an inherited blood disorder that occurs if both the maternal and paternal copies of the hbb gene are defective. in other words, if an individual receives just one copy of the defective hbb gene, either from mother or father, then the individual has no sickle cell anaemia but has what is called “sickle cell trait”. people with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. three inheritance scenarios can lead to a child having sickle cell anaemia : — both parents have sickle cell trait — one parent has sickle cell anaemia and the other has sickle cell trait — both parents have sickle cell anaemia the following statements are drawn as conclusions from the above data (kenya). i. patients with scd (sickle cell disease) are less likely to be infected with malaria. ii. patients with scd (sickle cell disease) are more likely to be infected with malaria. iii. over the years the percentage of people infected with malaria has been decreasing. iv. year 2000 saw the largest percentage difference between malaria patients with and without scd. choose from below the correct alternative..

• A. only I is true
• B. I and IV are true
• C. III and II are true
• D. I and III are true

Direction: Read the following text and answer the following questions on the basis of the same : Sickle cell anaemia is a genetic disorder where the body produces an abnormal haemoglobin called haemoglobins. Red blood cells are normally flexible and round, but when the haemoglobin is defective, blood cells take on a “sickle” or crescent shape. Sickle cell anaemia is caused by mutations in a gene called HBB. It is an inherited blood disorder that occurs if both the maternal and paternal copies of the HBB gene are defective. In other words, if an individual receives just one copy of the defective HBB gene, either from mother or father, then the individual has no sickle cell anaemia but has what is called “sickle cell trait”. People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. Three inheritance scenarios can lead to a child having sickle cell anaemia : — Both parents have sickle cell trait — One parent has sickle cell anaemia and the other has sickle cell trait — Both parents have sickle cell anaemia If both parents have sickle cell trait, then there is _______________of the child having sickle cell anaemia.

If both parents have sickle cell trait, then there is a **25% chance** of the child having sickle cell anaemia.

Solution: When both parents have the sickle cell trait, they can pass on either a normal gene or the mutated gene to their child. The possible combinations are:

1. Normal gene from both parents (25% chance) 2. Mutated gene from one parent and normal gene from the other (50% chance - child becomes a carrier like the parents) 3. Mutated gene from both parents (25% chance - child has sickle cell anaemia)

So, there is a 25% probability that the child will inherit the mutated gene from both parents and, therefore, have sickle cell anaemia.

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Direction: Read the following text and answer the following questions on the basis of the same : Sickle cell anaemia is a genetic disorder where the body produces an abnormal haemoglobin called haemoglobins. Red blood cells are normally flexible and round, but when the haemoglobin is defective, blood cells take on a “sickle” or crescent shape. Sickle cell anaemia is caused by mutations in a gene called HBB. It is an inherited blood disorder that occurs if both the maternal and paternal copies of the HBB gene are defective. In other words, if an individual receives just one copy of the defective HBB gene, either from mother or father, then the individual has no sickle cell anaemia but has what is called “sickle cell trait”. People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. Three inheritance scenarios can lead to a child having sickle cell anaemia : — Both parents have sickle cell trait — One parent has sickle cell anaemia and the other has sickle cell trait — Both parents have sickle cell anaemia If one parent has sickle cell anaemia and the other has sickle cell trait, there is __________that their children will have sickle cell anaemia and ___________will have sickle cell trait.

• A. 25 % risk, 75% risk
• B. 50 % risk, 50% risk
• C. 75% risk, 25% risk

Direction: Read the following text and answer the following questions on the basis of the same :

Sickle cell anaemia is a genetic disorder where the body produces an abnormal haemoglobin called haemoglobins. Red blood cells are normally flexible and round, but when the haemoglobin is defective, blood cells take on a “sickle” or crescent shape. Sickle cell anaemia is caused by mutations in a gene called HBB.

It is an inherited blood disorder that occurs if both the maternal and paternal copies of the HBB gene are defective. In other words, if an individual receives just one copy of the defective HBB gene, either from mother or father, then the individual has no sickle cell anaemia but has what is called “sickle cell trait”. People with sickle cell trait usually do not have any symptoms or problems but they can pass the mutated gene onto their children. Three inheritance scenarios can lead to a child having sickle cell anaemia :

— Both parents have sickle cell trait

— One parent has sickle cell anaemia and the other has sickle cell trait

— Both parents have sickle cell anaemia

Sickle cell anaemia is a/an ________________ disease.

• A. X linked
• B. autosomal dominant
• C. autosomal recessive
• D. Y linked

If both parents have sickle cell trait, then there is _______________of the child having sickle cell trait.

• A. 25 % risk
• B. 50 % risk
• C. 75% risk

Read the following and answer the questions given below:

Turner’s syndrome is an example of monosomy. It is formed by the union of an allosome free egg and a normal ‘X’ containing sperm or a normal egg and an allosome free sperm. The individual has 2n = 45 chromosomes (44 + X0) instead of 46. Such individuals are sterile females who have rudimentary ovaries, under developed breasts, small uterus, short stature, webbed neck and abnormal intelligence. They may not menstruate or ovulate. This disorder can be treated by giving female sex hormone to the women from the age of puberty to make them develop breasts and have menstruation. This makes them feel more normal.

Assertion : Turners syndrome is caused due to absence of any one of the X and Y sex chromosome.

Reason : Individuals suffering from Turner 'syndrome show masculine as well as feminine development.

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of assertion.
• C. Assertion is true but reason is false.
• D. Both assertion and reason are false.

Turner’s syndrome is an example of

• A. aneuploidy
• B. euploidy
• C. polyploidy
• D. autosomal abnormality.

Which of the following statements regarding Turner’s syndrome is incorrect?

• A. It is a case of monosomy of chromosomes.
• B. The suffering individual is a sterile female having one ‘X’ chromosome missing in the cells.
• C. The problem is due to an extra chromosome.
• D. The individual are of short stature.

Number ot barr body present in a female with Turners syndrome is

Turner’s syndrome is a/an

• A. autosomal recessive Mendelian disorder
• B. autosomal dominant Mendelian disorder
• C. sex linked Mendelian disorder
• D. chromosomal disorder.

Haemophilia is a sex linked disease which is also known as bleeder’s disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of anti-haemophilic globulin or factor VIII and plasma thromboplastin factor IX essential for it. As a result of continuous bleeding the patient may die of blood loss. Colour blindness is another type of sex linked trait in which the eye fails to distinguish red and green colours. Vision is however, not affected and the colour blind can, lead a normal life, reading, writing and driving (distinguishing traffic lights by their position).

Anup is having colourblindness and is married to Soni who is normal. What is the chance that their son will have the disease?

Colour blindness is a sex-linked recessive disorder, which results in defects in either red or green cone of an eye which ultimately leads to the failure in discriminating between red and green colour. The gene for colour blindness is located on X-chromosome.

If a colourblind man marries a normal women the chances for their son to be colourblind is 0% because son will receive X-chromosome from his mother (who is not colourblind) and Y from the father (as gene of colour blindness is present on X, so Y chromosome is not affected at all). Thus, there is no chance for their son to be affected. Infact their girl child (daughter) will be the carrier of the disease.

Haemophilia is a sex linked disease which is also known as bleeder’s disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of anti-haemophilic globulin or factor VIII and plasma thromboplastin factor IX essential for it. As a result of continuous bleeding the patient may die of blood loss. Colour blindness is another type of sex linked trait in which the eye fails to distinguish red and green colours. Vision is however, not affected and the colour blind can, lead a normal life, reading, writing and driving (distinguishing traffic lights by their position).

A man whose father was colourblind and mother was normal marries a woman whose father was haemophilic and mother was normal. Which of the following is true for their progenies? [Note: Percentage is from the total number of progenies.]

• A. 25% female progenies carry the gene for both haemophilia and colourblindness.
• B. 25% male progenies carry only the gene of colourblindness.
• C. 25% female progenies carry only the gene of colourblindness.
• D. 25% male progenies and 25% female progenies carry the gene of haemophilia.

If a haemophilic man marries a woman whose father was haemophilic and mother was normal then which of the following holds true for their progenies?

• A. Of the total number of daughters, 50% daughters are carrier and 50% are haemophilic.
• B. All the daughters are haemophilic.
• C. All sons are haemophilic and all daughters are normal.
• D. All sons are normal, all daughters are carriers.

Which of the following statements is incorrect regarding haemophilia?

• A. It is a dominant disease.
• B. A single protein involved in clotting of blood is affected.
• C. It is recessive disease.
• D. It is Mendelian disorder.

Directions: In the following questions, a statement of assertion is followed by a statement of reason.

Assertion: In F 2 generation of plant Mirabilis jalapa, the pink coloured flowers appear.

Reason: This is observed due epistatic suppression of white colour alleles in one of parental flowers by red colour alleles.

• A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
• B. If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
• C. If Assertion is true but Reason is false.
• D. If both Assertion and Reason are false.

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Important Questions for Case Based Questions Test: Principles of Inheritance & Variation - 2

Case based questions test: principles of inheritance & variation - 2 mcqs with answers, online tests for case based questions test: principles of inheritance & variation - 2.

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