Class 10 Biology - Heredity and Evolution - Exercises

Multiple Choice Questions

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as: (a) TTWW (b) TTww (c) TtWW (d) TtWw Answer: (c) TtWW. Reason: Since all progeny bore violet flowers, violet (W) must be dominant and the parent must be homozygous (WW) for it. Since half the progeny were short, the tall parent must have a recessive allele for shortness (t), making it heterozygous (Tt).

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Short and Long Answer Questions

2. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? Answer: No, we cannot conclude whether the trait is dominant or recessive based on this information alone. To determine dominance, we need to know the outcome of a cross between two different traits (e.g., light eyes and dark eyes) and see which one is expressed in the F1 generation. The fact that light-eyed parents have light-eyed children only shows that the trait is inheritable, but it doesn't reveal the relationship between different alleles.

3. Outline a project which aims to find the dominant coat colour in dogs. Answer:

• Objective: To identify the dominant coat color allele in a specific breed of dogs (e.g., Black vs. Brown).
• Procedure:
  1. Select a pure-bred black dog and a pure-bred brown dog.
  2. Cross these two dogs to produce the first generation (F1).
  3. Observe the coat color of all the F1 puppies.
  4. The color that appears in all (or the vast majority of) F1 puppies is the dominant trait.
  5. Further, cross two F1 individuals to see if the other color reappears in the F2 generation in a roughly 3:1 ratio, confirming the Mendelian pattern of inheritance.

4. How is the equal genetic contribution of male and female parents ensured in the progeny? Answer: Equal genetic contribution is ensured through the process of meiosis and fertilization:

• During meiosis, specialized germ-cells (gametes) are formed, which contain only half the number of chromosomes (one set) compared to normal body cells.
• In humans, both the sperm (from the father) and the egg (from the mother) contribute 23 chromosomes each.
• When fertilization occurs, the sperm and egg fuse to form a zygote, restoring the full set of 46 chromosomes (23 pairs). Thus, the offspring receives an equal amount of genetic material from both parents.

5. How is the sex of the child determined in human beings? Answer: In humans, sex is determined genetically:

• Women have a perfect pair of sex chromosomes, XX.
• Men have a mismatched pair, XY.
• All children inherit an X chromosome from their mother.
• The sex of the child depends on whether they inherit an X chromosome from the father (becoming a girl, XX) or a Y chromosome from the father (becoming a boy, XY). Thus, the father's contribution determines the sex.