🧬 UNIT – 8 : HEREDITY(Question)

🧬 UNIT – 8 : HEREDITY

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Learning Points

• Combination of differences during reproduction

• Heredity and inherited traits

• Mendel’s laws of inheritance

• Sex determination in humans

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I. Multiple Choice Questions (1 mark each)

1. He is called the father of modern genetics.
   A) Mendeleev B) Gregor Mendel C) Lemarck D) Charles Darwin

2. The plant used by Mendel for his experiments is
   A) Rose B) Pea C) Hibiscus D) Sunflower

3. The ratio of tall and short plants obtained in Mendel’s monohybrid cross was
   A) 2 : 1 B) 9 : 3 : 3 : 1 C) 3 : 1 D) 1 : 1

4. When a pure tall pea plant is crossed with a pure short one, what is the ratio of pure tall to pure short in the F₂ generation?
   A) 1 : 3 B) 3 : 1 C) 1 : 1 D) 2 : 1

5. The transfer of traits from parents to offspring is called
   A) DNA replication B) Mutation C) Transposition D) Heredity

6. The factors that determine the sex of a male child are
   A) XX B) XY C) YY D) All of these

7. When a tall pea plant is crossed with a short one, all offspring are tall because
   A) Trait for height is dominant
   B) Trait for height is recessive
   C) Both parents are tall
   D) Both parents are short

8. In Mendel’s experiment, when tall purple plants were crossed with dwarf white plants, the F₁ generation had all purple plants but some were tall and some short. The genetics of the tall plant is
   A) TTWW B) ttww C) TtWw D) TTww

9. A trait that appears in all generations is
   A) Dominant B) Recessive C) Acquired D) Intermediate

10. The molecule that carries genetic information is
    A) Gene B) Chromosome C) DNA D) Ribosome

11. The method of reproduction used by Mendel to obtain F₂ generation was
    A) Self-pollination B) Cross-pollination C) Artificial pollination D) Hybridization

12. The generation in which Mendel used cross-pollination is
    A) F₁ B) F₂ C) P D) F₃

13. When round yellow (RRYY) plants are crossed with wrinkled green (rryy), the number of round green seeds in the F₁ generation is
    A) 16 B) 8 C) 4 D) 0

14. When round green (RRyy) plants are crossed with wrinkled yellow (rrYY), the seeds obtained in the F₁ generation are
    A) Round and green B) Round and yellow C) Wrinkled and green D) Wrinkled and yellow

15. Pea plants with round seeds (RR) were crossed with wrinkled seeds (rr). The percentage of offspring with RR in the F₂ generation is
    A) 50% B) 75% C) 25% D) 0%

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II. One Mark Questions

16. Write the indicator of the trait having green seeds and flowers at the top of the stem.

17. What is the sex of a child born when the father contributes an X chromosome?

18. Why is the father responsible for determining the sex of a child?

19. What is the ratio of expressed forms of plants in Mendel’s monohybrid cross?

20. What is the ratio of gene pattern in a monohybrid cross?

21. Is cross-pollination possible in flowers having only stamens?

22. Why are changes in body cells not inherited?

23. What is a gene?

24. What is heredity?

25. How is the sex of a male child determined?

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III. Two Mark Questions

26. What is a monohybrid cross? Write the phenotypic ratio in F₂ generation.

27. What is a dihybrid cross? Write the ratio obtained in F₂ generation.

28. Define dominant and recessive traits with examples.

29. In a cross of tall red (TTRR) and short white (ttrr) pea plants, write the genotype of F₁ and F₂ generations.

30. Why are variations in sexual reproduction greater than in asexual reproduction?

31. Write one difference between male and female sex chromosomes.

32. In an experiment on dogs, the colour of the coat is controlled by genes B and b. When two heterozygous dogs were crossed, what was the expected ratio of white and black dogs?

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IV. Three Mark Questions

33. In a cross between pure tall (TT) and pure dwarf (tt) pea plants,
    a) What are the results obtained in F₁ and F₂ generations?
    b) Write the genotypic and phenotypic ratios.

34. What are the results obtained in a dihybrid cross between plants differing in two traits — shape and colour of seeds?

35. In pea plants, red colour (R) is dominant over white (r). When two plants with genotypes Rr and Rr are crossed, write the expected results with Punnett square.

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V. Four Mark Questions

36. Explain Mendel’s law of segregation with a suitable example.

37. Explain Mendel’s law of independent assortment using a dihybrid cross.

38. Describe the process of sex determination in human beings with a diagram.

39. Write a short note on DNA and its role in heredity.

40. Define and differentiate between inherited and acquired traits with examples.

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I. Multiple Choice Questions (1 mark each)

Q.No	Correct Answer	Explanation
1	✅ B. Gregor Mendel	Father of modern genetics
2	✅ B. Pea	Plant chosen by Mendel for experiments
3	✅ C. 3 : 1	Phenotypic ratio in monohybrid cross
4	✅ C. 1 : 1	Ratio of pure tall to pure short in F₂
5	✅ D. Heredity	Transmission of traits from parents to offspring
6	✅ B. XY	Male child determined by XY chromosomes
7	✅ A. Trait for height is dominant	Dominant gene expresses itself
8	✅ C. TtWw	Hybrid genotype of tall purple plants
9	✅ A. Dominant	Appears in all generations
10	✅ C. DNA	Molecule carrying genetic information
11	✅ A. Self-pollination	Used to obtain F₂ generation
12	✅ A. F₁	Cross-pollination used to form F₁ generation
13	✅ D. 0	All F₁ plants are round yellow (no green)
14	✅ B. Round and yellow	Dominant traits expressed in F₁
15	✅ C. 25%	Homozygous dominant RR in F₂ generation

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II. One Mark Questions – Key Answers

16. Indicator: Ggaa (green seeds and terminal flowers).

17. Sex: Female (XX).

18. Reason: Father provides either X or Y chromosome, deciding child’s sex.

19. Phenotypic ratio: 3 tall : 1 dwarf.

20. Genotypic ratio: 1 TT : 2 Tt : 1 tt.

21. No, because flower has only stamens and no pistil.

22. Body cell changes not inherited – only gametic (reproductive cell) changes pass to offspring.

23. Gene: Segment of DNA controlling expression of a trait.

24. Heredity: Transmission of characters from parents to offspring.

25. Sex determination:
     If sperm contributes Y → Male (XY);
     If sperm contributes X → Female (XX).

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III. Two Mark Questions – Key Answers

26. Monohybrid cross:
    Cross involving one trait (e.g., tall × dwarf).
    Phenotypic ratio = 3 : 1 (F₂).

27. Dihybrid cross:
    Cross involving two traits (e.g., round yellow × wrinkled green).
    F₂ ratio = 9 : 3 : 3 : 1.

28. Dominant trait: Expressed when one allele present (e.g., tallness).
    Recessive trait: Expressed only when both alleles same (e.g., dwarfness).

29. F₁: TtRr (tall red).
    F₂: 9 tall red : 3 tall white : 3 short red : 1 short white.

30. Sexual reproduction → greater variation due to DNA recombination and gamete fusion.

31. Male: XY  Female: XX.

32. Dogs cross:
    1 white : 2 grey : 1 black
    (Genotypic ratio 1 : 2 : 1).

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IV. Three Mark Questions – Key Answers

33. Monohybrid cross (TT × tt):
    F₁ – All tall (Tt).
    F₂ – Genotypic ratio 1:2:1; Phenotypic ratio 3:1.

34. Dihybrid cross (RRYY × rryy):
    F₂ phenotypic ratio = 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.

35. Red × Red (Rr × Rr):
    Punnett square → 1 RR : 2 Rr : 1 rr →
    Phenotypic ratio = 3 red : 1 white.

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V. Four Mark Questions – Key Answers

36. Mendel’s Law of Segregation:
    Two alleles separate during gamete formation, so each gamete carries only one allele.
    Example: TT × tt → F₁ Tt → F₂ (1:2:1).

37. Mendel’s Law of Independent Assortment:
    When two traits are considered, they are inherited independently.
    Example: Round yellow × wrinkled green → 9:3:3:1 ratio.

38. Sex determination in humans:
    Father (XY) – determines sex.
    Mother (XX) – contributes only X.
    X from father → girl (XX), Y from father → boy (XY).
    (Diagram of cross to be drawn.)

39. DNA and Heredity:
    DNA carries genetic information; controls inheritance through replication and gene expression.

40. Inherited vs Acquired traits:

Inherited	Acquired
Passed from parents	Developed during lifetime
Controlled by genes	Not genetic
Eg: Eye colour	Eg: Knowledge, scars