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Principles of Inheritance and Variation Class 12 Biology MCQs Pdf
1. When ‘Aa’ is crossed with ‘aa’, (A is dominant over a)
(a) all the offspring will have dominant phenotype.
(b) all the offspring will have recessive phenotype.
(c) 50% of offspring will have dominant phenotype and 50% will have recessive phenotype.
(d) 75% of offspring will have dominant phenotype and 50% will have recessive phenotype.
Answer
Answer: c
2. A heterozygous violet-flowered pea plant is crossed to another homozygous violet- flowered pea plant. What percent of the progeny plants will have the recessive trait, i.e., white flowers?
(a) 0%
(b) 25%
(c) 50%
(d) 75%
Answer
Answer: a
3. From a cross AABb x aaBb, the genotypes AaBB : AaBb : Aabb will be obtained in the ratio
(a) 1:1:2
(b) 1:2:1
(c) 2:1:1
(d) 2:1:2
Answer
Answer: b
4. The possibility of all genotypes of offspring in a genetic cross is calculated by a graphical representation which was developed by
(a) Komberg
(b) T.H. Morgan
(c) Gregor Mendel
(d) Reginald Punnett
Answer
Answer: d
5. A woman with normal vision has a colorblind father. She marries a colourblind man. What proportion of their children will be colourblind?
(a) 0%
(b) 25%
(c) 50%
(d) 100%
Answer
Answer: c
6. Study the pedigree chart given
Select the correct option about the conclusion.
(a) It is a sex-linked recessive trait.
(b) It is an autosomal recessive trait.
(c) It is an autosomal dominant trait.
(d) It is a sex-linked dominant trait.
Answer
Answer: b
7. Mother and father of a person with ‘O’ blood group have ‘A’ and ‘B’ blood group respectively. What would be the genotype of both mother and father? [NCERT Exemplar]
(a) Mother is homozygous for ‘A’ blood group and father is heterozygous for ‘B’.
(b) Mother is heterozygous for ‘A’ blood group and father is homozygous for ‘B’.
(c) Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively.
(d) Both mother and father are homozygous for ‘A’ and ‘B’ blood group, respectively.
Answer
Answer: c
8. The inheritance pattern of a gene over generations among humans is studied by the pedigree analysis. Character studied in the pedigree analysis is equivalent to: [NCERT Exemplar]
(a) Quantitative trait.
(b) Mendelian trait.
(c) Polygenic trait.
(d) Maternal trait.
Answer
Answer: b
9. Occasionally, a single gene may express more than one effect. The phenomenon is called: [NCERT Exemplar]
(a) multiple allelism
(b) mosaicism
(c) pleiotropy
(d) polygeny.
Answer
Answer: c
10. Conditions of a karyotype 2n ± 1 and 2n ± 2 are called: [NCERT Exemplar]
(a) Aneuploidy
(b) Polyploidy
(c) Allopolyploidy
(d) Monosomy.
Answer
Answer: a
11. If a genetic disease is transferred from a phenotypically normal but carrier female to only some of the male progeny, the disease is: [NCERT Exemplar]
(a) Autosomal dominant
(b) Autosomal recessive
(c) Sex-linked dominant
(d) Sex-linked recessive.
Answer
Answer: d
12. In a dihybrid cross, if you get 9:3:3:1 ratio it denotes that: [NCERT Exemplar]
(a) The alleles of two genes are interacting with each other.
(b) It is a multigenic inheritance.
(c) It is a case of multiple allelism.
(d) The alleles of two genes are segregating independently.
Answer
Answer: d
13. In sickle cell anaemia glutamic acid is ’» replaced by valine. Which one of the following triplets codes for valine? [NCERT Exemplar]
(a) G G G
(b) A A G
(c) G A A
(d) G U G
Answer
Answer: d
14. Which of the following traits studied by Mendel in garden pea is a dominant trait?
(a) Terminal flowers.
(b) Inflated pod.
(c) Green colour of seed.
(d) Yellow colour of pod.
Answer
Answer: b
15. If a haemophilic woman marries a normal man,
(a) all their children will be normal.
(b) all their sons will be haemophilic.
(c) all their daughters will be haemophilic.
(d) 50% sons and 50% daughters will be haemophilic.
Answer
Answer: b
16. Trisomy of 21 st chromosome in a male, leads to ______ syndrome.
Answer/Explanation
Answer:
Explaination: Down’s.
17. Sex chromosome complement of a female bird is ______ .
Answer/Explanation
Answer:
Explaination: ZW.
18. If three children in a family have blood groups O, AB and A, the genotypes of the parents must be _____ and ____ .
Answer/Explanation
Answer:
Explaination: IAi, IBi.
19. Mendel’s law of ______ explains the expression of only one form of the trait in F, hybrid.
Answer/Explanation
Answer:
Explaination: Dominance.
20. XO chromosomal abnormality in humans _______ causes syndrome.
Answer/Explanation
Answer:
Explaination: Turner’s.
21. was the first to observe the X-chromosome in a few insects.
Answer/Explanation
Answer:
Explaination: Henking.
22. The physical association between two genes on a chromosome, is termed as _____ by Morgan.
Answer/Explanation
Answer:
Explaination: Linkage.
23. Female heterogamety is observed in
Answer/Explanation
Answer:
Explaination: Birds.
24. Cystic fibrosis and haemophilia are examples of disorders.
Answer/Explanation
Answer:
Explaination: Mendelian.
25. In sickle-cell anaemia, the amino acid, glutamic acid is substituted by in the beta chain of haemoglobin.
Answer/Explanation
Answer:
Explaination: Valine.
26. Match the items in Column I with those in Column II.
| Column I | Column II |
| A. ABO blood group in humans. | 1. Polygenic inheritance. |
| B. Flower colour snapdragon. | 2. Mendelian genetic disorder. |
| C. Human skin colour. | 3. Sex-linked Mendelian disorder |
| D. Phenyl – ketonuria. | 4. Incomplete dominance |
| 5. Multiple allelism. |
Answer/Explanation
Answer:
Explaination: A – 5, B – 4, C – 1, D – 2
27. Match the sex-chromosome complements in Column I with the male/female organisms in Column II.
| Column I | Column II |
| A. XO | 1. Human male |
| B. XX | 2. Male bird |
| C. XY | 3. Male grasshopper |
| D. ZZ | 4. Female Drosophila |
| 5, Female bird |
Answer/Explanation
Answer:
Explaination: A – 3, B – 4, C – 1, D – 5
28. The recessive trait appears only under homozygous condition. [True/False]
Answer/Explanation
Answer:
Explaination: True.
29. The phenotype of the F1 hybrid resembles the dominant parent, when there is incomplete dominance. [True/False]
Answer/Explanation
Answer:
Explaination: False.
30. The cross between the F1 hybrid with a homozygous dominant individual, is called a test cross. [True/False]
Answer/Explanation
Answer:
Explaination: False.
31. Mendel could not have framed the law of independent assortment, if the genes he had studied, showed linkage. [True/False]
Answer/Explanation
Answer:
Explaination: True.
32. 9:3 :3 :1 is the genotypic ratio of a Mendelian dihybrid cross. [True/False]
Answer/Explanation
Answer:
Explaination: True.
Directions (Q33 to Q35): Mark the odd one in each of the following groups.
33. Phenyl ketonuria, Sickle-cell anaemia, Cystic fibrosis, Colourblindness
Answer/Explanation
Answer:
Explaination: Colourblindness.
34. Inflated pods, Terminal flowers, Yellow seeds, Green pods (all in garden pea).
Answer/Explanation
Answer:
Explaination: Terminal flowers.
35. Turner’s syndrome, Klinefelter’s syndrome, Down’s syndrome, Haemophilia.
Answer/Explanation
Answer:
Explaination: Haemophilia.
36. Define inheritance.
Answer/Explanation
Answer:
Explaination: Inheritance is defined as the process by which characters are passed on from one generation to the next.
37. What is genetics?
Answer/Explanation
Answer:
Explaination: Genetics is the branch of science that deals with inheritance and variation of traits.
38. What are true-breeding lines that are used to study inheritance pattern of traits in plants? [Delhi 2014]
Answer/Explanation
Answer:
Explaination: A true-breeding line is one that has undergone continuous self-pollination/inbreeding and shows stable inheritance and expression of a trait for several generations.
39. List any two characters of pea plants used by Mendel in his experiments, other than height of the plant and colour of the seed. [Delhi 2017C]
Answer/Explanation
Answer:
Explaination: Colour of the pod, shape of the pod, colour
of the flower, position of the flower, shape of the seed. (any two)
40. Name two contrasting pod-related traits studied by Mendel, in pea plant experiments. [AI 2011C]
Answer/Explanation
Answer:
Explaination:
– Pod colour: Green pods and yellow pods.
– Pod shape: Inflated pods and constricted pods. (anyone)
41. Mention two contrasting flower-related traits studied by Mendel in pea plant experiments. [AI 2011C]
Answer/Explanation
Answer:
Explaination:
– Flower position: Axial flowers and terminal flowers
– Flower colour: Violet flowers and white flowers. (any one)
42. Mention any two contrasting traits with respect to seeds in pea plants that were studied by Mendel. [AI 2014]
Answer/Explanation
Answer:
Explaination:
– Seed shape: Round and wrinkled.
– Seed colour: Yellow and green, (any one)
43. What is the proof for or what indicates that the characters Mendel studied did not show blending? [HOTS]
Answer/Explanation
Answer:
Explaination: The parental forms of the trait appear without any change in the F2 generation.
44. What is meant by blending inheritance?
Answer/Explanation
Answer:
Explaination: Blending inheritance is the phenomenon in which the expression of a trait is due to mixing or blending of the parental characters and the trait expressed is in between the two parental forms of the trait; the parental forms of the trait never reappear in the subsequent progenies.
45. State a difference between a gene and an allele. [Delhi 2016]
Answer/Explanation
Answer:
Explaination:
– A gene is a unit of inheritance, which contains information that is required to express a particular trait in an organism.
– An allele is one of the slightly different forms of a gene that codes for a contrasting trait.
46. What is meant by genotype?
Answer/Explanation
Answer:
Explaination: The genetic constitution of an organism, is called its genotype.
47. What is phenotype?
Answer/Explanation
Answer:
Explaination: The observable or external appearance of a character of an organism, is its phenotype.
48. Mention the type of allele which expresses itself only in homozygous condition in an organism. [Foreign 2011]
Answer/Explanation
Answer:
Explaination: Recessive allele.
49. What is a monohybrid cross?
Answer/Explanation
Answer:
Explaination: Monohybrid cross is a cross made between , two individuals of a species, considering the inheritance of the contrasting pair of a single character/trait.
50. Why is a plant with genotype Tt referred to as heterozygous? [HOTS]
Answer/Explanation
Answer:
Explaination: Since the alleles for the contrasting forms of a trait are dissimilar, it is referred to as heterozygous.
51. State the fate of a pair of autosomes during gamete formation. [Delhi 2017]
Answer/Explanation
Answer:
Explaination: The members of a pair of autosomes segregate during gamete formation and enter different gametes.
52. British geneticist R.C. 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/Explanation
Answer:
Explaination: This graphical representation predicts the probability of all possible genotypes of offspring in the genetic cross carried out.
53. Write the percentage of the pea plants that would be homozygous recessive in the F2 generation, when tall F1 heterozygous pea plants are selfed. [Delhi 2012C]
Answer/Explanation
Answer:
Explaination: 25 per cent.
54. Write the percentage of the pea plants that would be heterozygous tall in the F2 generation, when the tall heterozygous F1 pea plants are selfed. [Delhi 2012C]
Answer/Explanation
Answer:
Explaination: 50 per cent.
55. Write the percentage of F2 homozygous and heterozygous populations in a typical monohybrid cross. [Foreign 2010]
Answer/Explanation
Answer:
Explaination:
Homozygous population – 50 per cent.
Heterozygous population – 50 per cent.
56. When a tall pea plant was self-pollinated, one-fourth of the progeny were dwarf. Give the genotype of the parent and the dwarf progenies. [HOTS]
Answer/Explanation
Answer:
Explaination: Parent – Tt; Dwarf progenies – tt.
57. A garden pea plant
(A) produced inflated, yellow pods and another plant
(B) of the same species produced constricted, green pods. Identity the dominant traits. [Delhi 2012]
Answer/Explanation
Answer:
Explaination: Inflated pods and green pods are dominant traits.
58. A garden pea plant produced axial violet flowers. Another of the same species produced terminal violet flowers. Identify the dominant traits. [AI2012]
Answer/Explanation
Answer:
Explaination: Axial flowers and violet flowers are dominant traits.
59. A garden pea plant produced round, green seeds. Another of the same species produced wrinkled, yellow seeds. Identify the dominant traits. [Foreign 2012]
Answer/Explanation
Answer:
Explaination: Round seeds and yellow seeds are dominant traits.
60. Write the possible genotypes Mendel got, when he crossed F1 tall pea plant with a dwarf pea plant. [Foreign 2012; HOTS]
Answer/Explanation
Answer:
Explaination: Tt and tt.
61. Mendel observed two kinds of ratios, 3 : 1 and 1 : 2 : 1, in the F2 generation in his experiments on garden pea. Name these two ratios respectively.
Answer/Explanation
Answer:
Explaination:
3 : 1 is the phenotypic ratio of a monohybrid cross.
1 : 2 : 1 is the genotypic ratio of a monohybrid cross.
62. Name the type of cross that would help to find the genotype of a pea plant bearing violet flowers. [AI 2017]
Answer/Explanation
Answer:
Explaination: A test cross with a pea plant bearing white flowers.
63. In a test cross progeny of pea plants, all were bearing violet flowers. Give the genotypes of the parent pea plants. [AI 2012 C; HOTS]
Answer/Explanation
Answer:
Explaination: The genotypes of the parent pea plants are VV and vv.
64. Why in a test cross, did Mendel cross a tall pea plant with a dwarf pea plant only? [Foreign 2012; HOTS]
Answer/Explanation
Answer:
Explaination: Dwarfness is a recessive trait which is expressed only in homozygous condition; so, he was sure of the genotype of the dwarf plant as tt.
65. A cross was carried out between two pea plants showing the contrasting traits of height of the plant. The result of the cross showed 50% of parental characters. Name the type of cross. [CBSE Sample Paper 2018]
Answer/Explanation
Answer:
Explaination: It is a (monohybrid) test cross.
66. Name and state the law of Mendel, which explains the expression of only one of the parental characters in the F, progeny of a monohybrid cross. [HOTS]
Answer/Explanation
Answer:
Explaination: Law of dominance states that in a dissimilar pair of factors, one member of the pair dominates (dominant) the other (recessive).
67. Which law of inheritance of Mendel, is universally acceptable without any exception? State the law. [CBSE Sample Paper 2010; HOTS]
Answer/Explanation
Answer:
Explaination: Law of Segregation states that the members of the allelic pair that remained together in the hybrid, segregate or separate during gametogenesis and enter different gametes.
68. Name the type of inheritance in which the genotypic ratio is the same as the phenotypic ratio. Also give the ratio.
Answer/Explanation
Answer:
Explaination:
– Incomplete dominance is the phenomenon.
– The phenotypic and genotypic ratio of F2 progeny in a monohybrid cross is 1 : 2 : 1.
69. Name any one plant and its feature that shows the phenomenon of incomplete dominance.
Answer/Explanation
Answer:
Explaination: Snapdragon (Antirrhinum sps) shows incomplete dominance in the inheritance of its flower colour.
70. Give an example of a plant, where the F2 progeny of a monohybrid cross has the same genotypic and phenotypic ratios. [Delhi 2016C]
Answer/Explanation
Answer:
Explaination: Snapdragon (Antirrhinum sp.) shows same genotypic and phenotypic ratios for inheritance of flower colour.
71. Name the respective pattern of inheritance, where Ft phenotype
(a) does not resemble either of the two parents and is in between the two;
(b) resembles only one of the two parents. [AI 2012]
Answer/Explanation
Answer:
Explaination:
(a) Incomplete dominance.
(b) Complete dominance.
72. Write the technical term used in human ABO blood groups for IA, IB and i. [Delhi 2016C]
Answer/Explanation
Answer:
Explaination: Multiple alleles.
73. The gene I that controls the ABO blood grouping in human beings, has three alleles, IA, IB and i.
(a) How many different genotypes are likely to be present in the human population?
(b) Also, how many phenotypes are possibly present? [CBSE Sample Paper 2016]
Answer/Explanation
Answer:
Explaination:
(a) Six different genotypes.
(b) Four phenotypes.
74. Write the codominant alleles in the ABO blood group characteristic of humans.
Answer/Explanation
Answer:
Explaination: IA and IB are codominant alleles.
75. How many kinds of phenotypes would you expect in the F2 generation in a monohybrid cross, exhibiting codominance? [Delhi 2014]
Answer/Explanation
Answer:
Explaination: Three kinds of phenotypes.
76. Multiple allelism can be investigated only in populations. Justify. [HOTS]
Answer/Explanation
Answer:
Explaination: Though a gene exists in more than two allelic forms in multiple allelism, a person can have only two of those alleles, as he has only two sets of homologous chromosomes; so, multiple allelism can be studied only in a population.
77. How is pleiotropy exemplified in Drosophila?
Answer/Explanation
Answer:
Explaination: In Drosophila white eye colour is associated with depigmentation in many other parts of the body; it is due to the pleiotropic effect of a single gene.
78. What is a dihybrid cross?
Answer/Explanation
Answer:
Explaination: A dihybrid cross is a cross made between individuals of a species, considering the inheritance of contrasting pairs of two traits.
79. AaBb was crossed with aabb. What would be the phenotypic ratio of the progeny? Mention the term used to denote this kind of cross. [CBSE Sample Paper 2010]
Answer/Explanation
Answer:
Explaination:
– The phenotypic ratio will be 1 : 1 : 1 : 1. – It is a test cross.
80. 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/Explanation
Answer:
Explaination: A number of (successive) generations can be raised in a short time to study the patterns of inheritance.
81. Define linkage.
Answer/Explanation
Answer:
Explaination: Linkage is the phenomenon, where two or more linked genes are always inherited together and their recombination frequency in a dihybrid test cross progeny is less than 50%.
82. In a dihybrid cross carried out by T.H. Morgan in Drosophila, the F2 ratio deviated from that of Mendel’s dihybrid F22 ratio. Give a reason. [AI 2016C]
Or
Why do certain genes tend to be inherited together in a cell at the time of cell division? [HOTS]
Or
If the frequency of a parental form is higher than 25% in a dihybrid test cross, what does that indicate about the two genes involved? [HOTS]
Answer/Explanation
Answer:
Explaination: The genes show linkage and do not segregate independently of each other.
83. Morgan et al found that even on the same chromosome, recombination between some gene pairs was higher than that between some other gene pairs. Give reason for this observation.
Answer/Explanation
Answer:
Explaination: It is due to the distance between the gene pairs; more the distance, higher will be the recombination and vice versa.
84. If two genes are located far apart from each other, on a chromosome, how will the frequency of recombination get affected? [CBSE Sample Paper 2017,15]
Answer/Explanation
Answer:
Explaination:
– The two genes will segregate independently of each other and there will be 50% recombination.
85. Mention any two traits present on the X-chromosome of Drosophila.
Answer/Explanation
Answer:
Explaination: Eye colour, body colour, wing type. (any two)
86. Mention the contribution of genetic maps in human genome project. [AI 2011]
Answer/Explanation
Answer:
Explaination: The genetic maps were used as the starting point in the sequencing of whole genomes.
87. Do you think Mendel’s laws of inheritance would have been different if the characters he chose were located on the same chromosome? Why? [HOTS]
Answer/Explanation
Answer:
Explaination: Mendel could not have framed the law of independent assortment, if the genes for all the characters Mendel chose, were present on the same chromosome and showed the phenomenon of linkage.
88. Give an example of a polygenic trait in humans. [Delhi 2016C]
Answer/Explanation
Answer:
Explaination: Skin colour, intelligence, height, (any one)
89. Who suggested polygenic inheritance for the first time?
Answer/Explanation
Answer:
Explaination: Galton.
90. Give two examples of polygenic inheritances from plants.
Answer/Explanation
Answer:
Explaination:
(i) Cob length in maize.
(ii) Kernel colour in wheat.
91. Write the phenotypic ratio of the F2 progeny of a cross, involving polygenic trait controlled by three separate genes.
Answer/Explanation
Answer:
Explaination: 1 : 6 : 15 : 20 : 15 : 6 : 1.
92. On what basis is skin colour in humans considered polygenic? [AI 2015C]
Answer/Explanation
Answer:
Explaination: Skin colour in humans is controlled by three different genes and the phenotype is the cumulative effect of all the dominant alleles; hence, its inheritance is considered as polygenic.
93. Who first observed the X-chromosome? What was it called then?
Answer/Explanation
Answer:
Explaination: Henking first observed the X-chromosome. It was called X-body.
94. What are autosomes?
Answer/Explanation
Answer:
Explaination: All those chromosomes of an individual organism that are not involved in the determination of sex of that individual, are called autosomes.
95. Why is X-chromosome called sex chromosome?
Answer/Explanation
Answer:
Explaination: Since X-chromosome is involved in the determination of sex of an individual, it is called sex chromosome.
96. Give an example where
(a) males are XO and
(b) females are ZW.
Answer/Explanation
Answer:
Explaination:
(a) Grasshopper
(b) Fowls.
97. Theeggofan animal contains 10 chromosomes, of which one is X-chromosome. How many autosomes would there be, in the karyotype of this animal? [HOTS]
Answer/Explanation
Answer:
Explaination: 18 autosomes.
98. Give an example of an organism that exhibits haplodiploid sex determination system. [AI 2016C]
Answer/Explanation
Answer:
Explaination: Honeybee.
99. In a certain group of insects, some have 17 chromosomes and some have 18 chromosomes. Write about the gender of these two types of insects.
Answer/Explanation
Answer:
Explaination:
– Males have 17 chromosomes.
– Females have 18 chromosomes.
100. How many chromosomes do drones of honeybee possess? Name the type of cell division involved in the production of sperms by them. [AI 2015]
Answer/Explanation
Answer:
Explaination:
– Drones have 16 chromosomes.
– Mitosis occurs during production of sperms.
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