Principles of Inheritance and Variation: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. Name the scientist who first mapped genes.
2. Gametes produced by AaBbCc.
3. Give an example of pleiotropy.
4. Who discovered the X body?
5. Name the sex determination in birds.
6. Genotypes of group A.
7. Name a frameshift-causing change.
8. Karyotype of Klinefelter's syndrome.
9. Which amino acid replaces glutamic acid in Hb^S?
10. Recombination frequency of white–yellow genes in Drosophila.

D. Short answer I (2 marks each)

1. State the law of segregation.
2. Why is the law of segregation called the law of purity of gametes?
3. Distinguish linkage from recombination.
4. Explain haplodiploidy in honey bees.
5. Give two differences between Mendelian and chromosomal disorders.
6. Why are haemophilic females rare?
7. What is non-disjunction? Give one disorder it causes.
8. Why did Mendel's work remain unrecognised till 1900?

Rough work

E. Short answer II (3 marks each)

1. Work out a dihybrid test cross and give its ratio.
2. Explain the cause and symptoms of phenylketonuria.
3. Show by a cross how a colour-blind daughter can be born.
4. Describe Morgan's linkage experiment.
5. Compare Down's, Klinefelter's and Turner's syndromes.
6. Explain why the ABO blood group shows both co-dominance and dominance.

F. Long answer (5 marks each)

1. Explain Mendel's three laws with crosses.
2. Describe the genetic basis of sickle-cell anaemia and show by a cross how carrier parents may have an affected child.

G. HOTS (higher-order thinking)

1. Why do the genes for flower colour and seed shape in pea assort independently?
2. Two parents with normal colour vision have a colour-blind son. What are their genotypes?
3. Why is the F2 ratio of snapdragon not 3 : 1?
4. Can a person of group O be the father of a child of group AB? Explain.

20 MCQs

1. Mendel worked on
   (a) Drosophila (b) snapdragon (c) Pisum sativum (d) maize
2. F2 phenotypic ratio of a monohybrid cross
   (a) 3 : 1 (b) 1 : 2 : 1 (c) 9 : 3 : 3 : 1 (d) 1 : 1
3. Test cross ratio for a heterozygote
   (a) 3 : 1 (b) 9 : 3 : 3 : 1 (c) all dominant (d) 1 : 1
4. Gametes from AaBb
   (a) 2 (b) 4 (c) 8 (d) 16
5. Pink F1 in snapdragon shows
   (a) dominance (b) incomplete dominance (c) co-dominance (d) epistasis
6. Blood group AB shows
   (a) incomplete dominance (b) polygenic inheritance (c) pleiotropy (d) co-dominance
7. Number of genotypes in the ABO system
   (a) 6 (b) 4 (c) 3 (d) 9
8. Dihybrid F2 ratio
   (a) 3 : 1 (b) 1 : 1 : 1 : 1 (c) 9 : 3 : 3 : 1 (d) 1 : 2 : 1
9. The chromosomal theory was given by
   (a) Morgan (b) de Vries (c) Mendel (d) Sutton and Boveri
10. Gene mapping was first done by
    (a) Morgan (b) Sturtevant (c) Henking (d) Bateson
11. Human skin colour is an example of
    (a) pleiotropy (b) co-dominance (c) polygenic inheritance (d) multiple alleles
12. Female heterogamety is seen in
    (a) birds (b) humans (c) grasshopper (d) Drosophila
13. Drones of honey bee have
    (a) 32 chromosomes (b) 16 chromosomes (c) 8 (d) 64
14. Sickle-cell anaemia is due to
    (a) frameshift (b) deletion of a chromosome (c) point mutation (d) trisomy
15. Haemophilia is
    (a) autosomal dominant (b) autosomal recessive (c) Y-linked (d) X-linked recessive
16. Phenylketonuria results from lack of an enzyme converting
    (a) phenylalanine to tyrosine (b) tyrosine to phenylalanine (c) glucose to glycogen (d) none
17. Furrowed tongue and palm crease are seen in
    (a) Down's (b) Turner's (c) Klinefelter's (d) haemophilia
18. Klinefelter's karyotype
    (a) 45, XO (b) 46, XY (c) 47, +21 (d) 47, XXY
19. Thalassaemia is mainly
    (a) a qualitative defect (b) a quantitative defect of globin (c) X-linked (d) chromosomal
20. An O child is born to A and B parents; the parents are
    (a) I^AI^A, I^BI^B (b) I^AI^B, ii (c) I^Ai, I^Bi (d) I^Ai, I^BI^B

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: The F2 of a dihybrid cross shows 9 : 3 : 3 : 1. R: The two pairs of genes assort independently.
2. A: Group AB shows co-dominance. R: I^A and I^B are both expressed in the heterozygote.
3. A: Linked genes do not show 9 : 3 : 3 : 1. R: They lie on different chromosomes.
4. A: Haemophilic females are rare. R: The mother must be a carrier and the father haemophilic.
5. A: In birds the male decides the sex of the offspring. R: The female is ZW.
6. A: Down's syndrome is a Mendelian disorder. R: It is caused by an extra chromosome 21.

Key: 1 (a) · 2 (a) · 3 (c) · 4 (a) · 5 (d) · 6 (d)

Answers to the practice set