Principles of Inheritance and Variation | Class 12 Zoology | Sample Questions and Answers

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1 Score Questions

1. Which of the following is not a dominant trait?
    (a) Yellow seed 
    (b) Green pod
    (c) Terminal flower 
    (d) Round seed

2. Monohybrid F2 phenotypic ratio is

    (a) 1:2:1 
    (b) 3:1 
    (c) 1:1 
    (d) 9:3:3:1

3. Note the relationship between first two terms and fill up the fourth place.

    Mendel: Pisum sativum 
    Morgan: …………….

4. An inheritance in which heterozygous offspring shows intermediate character between two parental characteristics is called …………….

5. Human blood groups of ABO system have

    (a) 2 alleles
    (b) 3 alleles
    (c) 5 alleles 
    (d) 6 alleles

6. Which genotype of blood group shows co-dominance?

    (a) ii 
    (b) IAi
    (c) IBIB 
    (d) IAIB

7. Which of the following do not have similar sex chromosome (homogametic)?

    (a) Human female 
    (b) Drosophila female
    (c) Bird female 
    (d) Bird male

8. An analysis of genetic traits in several generations of a family is called …………….

9. A single gene exhibits multiple phenotypic expressions. It is called

    (a) Pleiotropy 
    (b) Multiple allelism
    (c) Co-dominance 
    (d) Polygenic inheritance

10. Chromosomal Theory of Inheritance was proposed by

    (a) Morgan 
    (b) Alfred Sturtevant
    (c) de Vries & Correns
    (d) Sutton & Boveri

11. Which of the following is not a Mendelian disorder?

Colour-blindness, Down's syndrome, Haemophilia, Thalassemia

12. ............... is a metabolic disorder that occurs due to lack of an enzyme that converts phenyl alanine to tyrosine.

13. Regarding Haemophilia (Royal disease), which of the following is wrong?

    a. Queen Victoria was not homozygous for the disease.
    b. It is more common in male than female.
    c. It is a chromosomal disorder affecting X chromosome.
    d. It is a sex-linked recessive disease.

14. Identify the syndrome from the genotypes given below:

    a. 44 Autosome + XXY 
    b. 44 Autosome +XO

2 Score Questions

15. A genetic cross is represented below.

    a. Identify the given cross.
    b. Mention the significance of such cross.

16. In Pea plant the gene for yellow seed colour is dominant over green and round seed shape is dominant over wrinkled. Write the four types of gametes formed in heterozygous pea plant with Yellow and round seeds (YyRr).

17. Observe the inheritance shown in A and B.

    a. Name the type of inheritance shown in A and B.
    b. What is the difference between the two types of inheritance?

18. The following table shows the F2 generation of a Dihybrid cross. Identify the phenotype with homozygous recessive genotype. Find out A: B: C: D.


No. of offspring (F2 gen.)









19. Study the following cross and answer the questions.

    a. Write the genotypes of Father, Mother and Son.
    b. Whether any change in blood group will occur if they have a daughter instead of son? Why?

20. Anil argues that if the father is ‘A’ blood group and mother is ‘B’ blood group, their children can only be ‘A’ group, ‘B’ group or ‘AB’ group. Do you agree with Anil’s argument? Give reason for your argument.

21. Drosophila is an ideal material for genetic study. Why? (Any 4 reasons).

22. Sex of the Baby is determined by the father, not by the mother. Substantiate.

23. The sudden heritable change occurring in the DNA sequence is called mutation.

    a. What are the different types of mutation? Briefly explain any one of them.
    b. Sickle cell anaemia is due to ………. mutation.

24. Observe the figure and answer the questions.

    a. Identify the syndromes A and B.
    b. What is the chromosome numbers in A and B?

25. Observe the diagram given below:

    a. Identify the syndrome. Write its karyotype.
    b. It occurs in both sexes. Write the reason.

26. Complete the table using suitable term.

Turner’s syndrome


Sterile female

(b) …………


(c) …………

(d) …………

Trisomy 21

Mental retardation

27. Symbols used in human pedigree analysis and their meanings are provided in the table. Fill in the blanks with suitable meaning or symbols.

28. Certain facts related to human disorder are given:
  • It is inborn error in metabolism.
  • It is inherited as an autosomal recessive trait.
  • The affected person is mentally retarded.
    a. Name the disorder.
    b. What are the physiological processes behind this mental retardation?

29. Diagrammatic representation of chromosome map of Drosophila is given below.

Y- Yellow W- White M- Miniature

    a. Which genes are more linked?
    b. Who mapped chromosome firstly?
    c. Tightly linked genes show low recombination. Why?

3 Score Questions

30. State Mendel’s Laws of inheritance.
31. Work of a student is given below:

    a. Mention any one genotype and phenotype.
    b. Complete the work using the Punnet square and find out the F2 phenotypic ratio.

32. Analyse the given pedigree charts.

    a. Identify the traits in figure A & B. Give one example for each.
    b. What show the shaded symbols used?

33. The beta globin chains of the haemoglobin molecule of two persons are given below.


    a. Which person has abnormal chain?
    b. Name the disorder affected him.
    c. Briefly explain the reason for that disorder

34. Some genetic abnormalities, their genotype and features are distributed in Column A, B and C respectively. Match them correctly.




Down’s syndrome

44 A + XO

Rudimentary ovary and sterility

Turner’s syndrome

44 A + XXY

Furrowed tongue and partially opened mouth

Klinefelter’s syndrome

45 A + XX/XY

Gynecomastia & sterility



1. (c) Terminal flower.
2. (b) 3:1
3. Drosophila melanogaster (Fruit fly).
4. Incomplete dominance.
5. (b) 3 alleles
6. (d) IAIB
7. (c) Bird female
8. Pedigree analysis.
9. (a) Pleiotropy
10. (d) Sutton & Boveri
11. Down's syndrome
12. Phenylketonuria.
13. (c) It is a chromosomal disorder affecting X chromosome.
14. (a) Klinefelter’s syndrome. (b) Turner’s syndrome.
15. (a) Test cross.
        (b) It is used to find out the unknown genotype of a character.
16. Gametes: YR, Yr, yR, yr.
17. (a) A= Mendelian inheritance. B= Co-dominance.
        (b) In Mendelian inheritance, one allele is dominant and the other is recessive.
    In Co-dominance, both alleles are dominant and together expressed in hybrid.
18. Genotype of B is homozygous recessive.
        A: B: C: D is 3: 1: 9: 3.
19. (a) Father: IAi, Mother: IBi, Son: ii 
(b) No. Because the gene of blood group is present in autosome not in sex chromosome. So there is no influence of sex in blood grouping.
20. No. Because if father and mother have heterozygous genotypes of blood groups (Father: IAi, Mother: IBi ), they can have O group offspring (ii).

21. It is the suitable material for genetic study because
  • They can grow on simple synthetic medium.
  • Short generation time (life cycle: 12-14 days).
  • Breeding can be done throughout the year.
  • Hundreds of progenies per mating.
22. Father (male) can produce 2 types of sperms- one with X chromosome and other with Y chromosome. Y chromosome is responsible for male child. Mother (female) can produce only ovum with X chromosome.

23. a) Point mutation and Frame shift mutation.
  • Point mutation: The mutation in a single base pair.
  • Frame-shift mutation: Deletion or insertion of base pairs resulting in the shifting of DNA sequences.
    b) Point mutation.

24. (a) A= Klinefelter’s syndrome. B= Turner’s syndrome.
        (b) A= 47 chromosomes. B= 45 chromosomes.
25. (a) Down’s syndrome. Genotype= 45A + XX/ XY.
        (b) Because it affects an autosome pair (21 trisomy). It is not a sex chromosomal problem.
26. (a) 44A + X0.
        (b) Klinefelter’s syndrome.
        (c) Feminine nature/ sterile male.
        (d) Down’s syndrome.
27. (a) Male. 
        (b) ¡ 
        (c) Sex unspecified. 
        (d) n
28. (a) Phenylketonuria.
    (b) Due to the lack of the enzyme phenylalanine hydroxylase, phenylalanine accumulates and converts into phenyl pyruvic acid and other derivatives. They accumulate in brain resulting in mental retardation.
29. (a) Genes of yellow body and white eye.
        (b) Alfred Sturtevant.
        (c) Tightly linked genes have no independent assortment or have low crossing over.
30. Mendel’s Laws of inheritance:

1. Law of Dominance:
    • Characters are controlled by factors.
    • Factors occur in pairs.
    • In a dissimilar pair of factors, one member of the pair dominates the other.
2. Law of Segregation: “During gamete formation, the factors (alleles) of a character pair present in parents segregate from each other such that a gamete receives only one of the 2 factors”.

3. Law of Independent Assortment: “When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters”.

31. (a) Genotype: RRYY, rryy or RrYy. Phenotype: Round yellow or Wrinkled green.
        (b) F2 phenotypic ratio: 9:3:3:1.

32. (a) A= Pedigree analysis of Autosomal dominant trait. E.g. Myotonic dystrophy.

        B= Pedigree analysis of Autosomal recessive trait. E.g. Sickle-cell anaemia.

(b) Shaded symbols represent affected individuals and show that the traits are affected to both male & female.

33. (a) Person A.
        (b) Sickle cell anaemia.
(c) The defect is caused by the substitution of Glutamic acid by Valine at the sixth position of the β-globin chain. This is due to the single base substitution at the sixth codon of the β-globin gene from GAG to GUG.




Down’s syndrome

45 A + XX/XY

Furrowed tongue and partially opened mouth

Turner’s syndrome

44 A + XO

Rudimentary ovary and sterility

Klinefelter’s syndrome

44 A + XXY

Gynecomastia & sterility    

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