Question Bank — Heredity

Section A — MCQs (1 mark each)

1. In a population of an asexually reproducing species, trait P is found in 25% of individuals while trait Q is found in 75%. Which trait most likely appeared first?
   (a) Trait P (b) Trait Q (c) Both appeared together (d) Cannot be determined

2. Mendel observed that in the F1 generation obtained by crossing tall and short pea plants, all plants were tall. This shows that
   (a) Tallness is recessive (b) Shortness is dominant (c) Tallness is dominant (d) Both traits blend

3. In human beings, the sex of a child is determined by the chromosome received from the
   (a) Mother only (b) Father only (c) Both parents equally (d) Environmental temperature

4. Assertion (A): In Mendel's F2 generation, both tall and short plants appear in the ratio 3:1.
   Reason (R): The F1 plants inherit both tallness and shortness factors, but only tallness is expressed.
   (a) Both A and R are true and R is the correct explanation of A
   (b) Both A and R are true but R is not the correct explanation of A
   (c) A is true but R is false (d) A is false but R is true

5. Assertion (A): Traits controlled by genes on separate chromosomes are inherited independently.
   Reason (R): Each chromosome carries only one gene.
   (a) Both A and R are true and R is the correct explanation of A
   (b) Both A and R are true but R is not the correct explanation of A
   (c) A is true but R is false (d) A is false but R is true

6. A section of DNA that provides information for making one protein is called
   (a) Chromosome (b) Gene (c) Hormone (d) Enzyme

7. In the cross between round-yellow and wrinkled-green pea plants, the F2 generation showed new combinations such as round-green and wrinkled-yellow. This demonstrates
   (a) Linkage of traits (b) Independent inheritance (c) Blending inheritance (d) Environmental influence

8. Which of the following is an example of a recessive trait in pea plants?
   (a) Tallness (b) Round seeds (c) Wrinkled seeds (d) Violet flowers

9. If both parents contribute a copy of the same gene, each germ cell must contain
   (a) Two copies of every gene (b) One copy of every gene (c) No genes (d) Only dominant genes

10. The mechanism that restores the normal number of chromosomes in the zygote is
    (a) Self-pollination (b) Fusion of two germ cells (c) Asexual reproduction (d) Environmental selection

Section B — Very Short Answer (2 marks each)

1. State the difference between dominant and recessive traits with one example from Mendel’s pea experiments.

2. Why do asexually reproducing organisms show very little variation compared to sexually reproducing organisms?

3. What is the role of DNA in the expression of traits such as plant height?

4. In human beings, why do all children inherit an X chromosome from the mother?

5. How do variations arise during reproduction and why are they important for survival?

6. What is the significance of the 3:1 ratio observed in the F2 generation of a monohybrid cross?

Section C — Short Answer (3 marks each)

1. Explain, with the help of a flow chart, how the F2 generation of a cross between tall and short pea plants shows both parental and new combinations of traits.

2. Describe how genes control characteristics such as height in plants.

3. Differentiate between the inheritance pattern of traits in sexually reproducing and asexually reproducing organisms.

4. Why is it that only the Y chromosome from the father determines the sex of a child in humans? Explain with a simple diagram description.

5. A tall plant with violet flowers is crossed with a short plant with white flowers. All F1 progeny are tall with violet flowers. What does this tell us about the nature of the traits? Predict the possible phenotypes in the F2 generation.

Section D — Long Answer (5 marks each)

1. Describe Mendel’s experiment on inheritance of traits using two contrasting characters (seed shape and seed colour). Explain how the results led to the conclusion that traits are inherited independently. Draw a labelled diagram showing the F1 and F2 generations and the phenotypic ratio obtained.

2. Explain with a labelled diagram how sex is determined in human beings. Why is the sex of the child determined by the father and not the mother?

3. How do traits get expressed? Taking the example of plant height, explain the role of genes, enzymes and hormones. Also state why both parents must contribute equally to the genetic material of the offspring.

Section E — Case/Source-Based (4 marks each)

Case 1

In a school activity, students noted the type of earlobes (free or attached) of all classmates and their parents. They found that free earlobes appeared in children even when one parent had attached earlobes, but attached earlobes appeared only when both parents had attached earlobes.

1. Which earlobe type is likely to be dominant? Give reason.
2. If both parents have free earlobes, can their child have attached earlobes? Why or why not?
3. How does this activity illustrate Mendelian inheritance?
4. What would be the expected ratio if two heterozygous free-earlobe parents have four children?

Case 2

A gardener crossed a plant having round green seeds with a plant having wrinkled yellow seeds. All F1 seeds were round and yellow. When F1 plants were self-pollinated, the F2 seeds showed four combinations: round-yellow, round-green, wrinkled-yellow and wrinkled-green in the ratio 9:3:3:1.

1. Identify the dominant traits for seed shape and colour.
2. Why did new combinations appear in the F2 generation?
3. What does the 9:3:3:1 ratio indicate about the inheritance of the two traits?
4. If the two traits had been linked on the same chromosome, what change would you expect in the F2 ratio?

Section F — HOTS and Application (3 marks each)

1. Predict-and-justify: What would happen to the phenotypic ratio in the F2 generation if the tallness factor in pea plants became lethal when present in two copies (TT)? Justify your answer.

2. Analyse an anomalous observation: In a monohybrid cross experiment, a student observed 100% tall plants in the F2 generation instead of the expected 3:1 ratio. Suggest a possible reason based on the chapter concepts and explain why this result deviates from Mendel’s findings.

3. Apply to an unfamiliar situation: In a certain reptile species, the temperature of the nest determines whether offspring develop as males or females. If climate change steadily raises nest temperatures, predict the likely change in sex ratio over generations and justify using the chapter’s ideas on variation and survival.

4. Compare two situations: Situation X: A bacterium divides asexually in a stable environment. Situation Y: The same species reproduces sexually during a sudden heat wave. In which situation is a heat-resistant variant more likely to appear and survive? Justify by comparing the sources of variation in both cases.