Chapter 8: Heredity

Multiple Choose Question and Answer :

Question :  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

[ The given information indicates a typical Mendelian dihybrid cross involving two traits: plant height (tall or short) and flower color (violet or white). The fact that almost half of the progeny were short suggests that the tall parent must be heterozygous for the trait of plant height. The resulting progeny would have a genotype of Tt (heterozygous for height) and WW (heterozygous for flower color).]

Short Question and Answer :

1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier? [2M]

Answer: Trait B is likely to have arisen earlier. In asexually reproducing species, new traits appear due to mutations and spread only through reproduction. A trait present in 60% of the population has had more time to pass from parent to offspring. Hence, it probably originated earlier than trait A (10%).

2. How does the creation of variations in a species promote survival? [2M]

Answer: Creation of variations helps a species to survive in changing environmental conditions. If climate, food availability, or diseases change, some individuals with useful variations can adjust better. They survive and reproduce, passing those traits to the next generation. Thus, variations increase the chances of survival of the species.

1. How do Mendel’s experiments show that traits may be dominant or recessive? [2M]

Answer: Mendel crossed pure tall pea plants with pure dwarf plants. In the F₁ generation, all plants were tall. The dwarf trait did not appear, but it was not lost.

When F₁ plants were self-pollinated, the F₂ generation showed tall and dwarf plants in 3:1 ratio. This proved that tallness is a dominant trait and dwarfness is a recessive trait, which appears only when both factors are recessive.

2. How do Mendel’s experiments show that traits are inherited independently? [2M]

Answer: Mendel performed a dihybrid cross using pea plants with two traits — seed shape (round/wrinkled) and seed colour (yellow/green). In F₁ generation, all seeds were round and yellow. In F₂ generation, four combinations appeared in 9:3:3:1 ratio, including new combinations like round green and wrinkled yellow. This showed that traits are inherited independently of each other.

3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not? [2M]

Answer: No, this information alone is not enough to decide which trait is dominant. The daughter has blood group O, which means she received one O allele from each parent. The mother is O, so her genotype is OO. The father, though showing blood group A, must be AO. This shows A is dominant over O, but we already know that from genetics, not just from this single case.

4. How is the sex of the child determined in human beings? [2M]

Answer: In human beings, the sex of the child is decided by the father. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The mother always gives an X chromosome through her egg. The father can give either an X or a Y through his sperm. If the child gets XX, it becomes a girl. If it gets XY, it becomes a boy. Hence, the sperm from the father determines the sex of the child.

Long Question and Answer :

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