Question 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?

Accepted Answer

Trait B is likely to have arisen earlier. In an asexually reproducing population, a trait present in a larger fraction of individuals has probably had more time to spread through reproduction.

Question 2

How does the creation of variations in a species promote survival?

Accepted Answer

Variations create differences among individuals. If environmental conditions change, some variations may give certain individuals a survival advantage, allowing them to reproduce and helping the species continue.

Question 3

How do Mendel's experiments show that traits may be dominant or recessive?

Accepted Answer

Mendel crossed pure tall pea plants with pure short pea plants. All F₁ plants were tall, showing that tallness was dominant over shortness. When F₁ plants self-pollinated, short plants reappeared in F₂, showing that the short trait was present but recessive.

Question 4

How do Mendel's experiments show that traits are inherited independently?

Accepted Answer

In a dihybrid cross, Mendel crossed pea plants differing in two traits, such as seed shape and colour. In F₂, new combinations appeared and the traits assorted in a 9:3:3:1 ratio. This showed that inheritance of one trait did not affect inheritance of the other.

Question 5

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?

Accepted Answer

No. This information alone is not enough to decide dominance. The father with blood group A must carry both A and O alleles (AO), while the mother is OO, so the daughter can be OO. To determine dominance, we need to know how alleles are expressed in heterozygous individuals; blood group A is expressed over O, but that cannot be concluded from only this family data.

Question 6

How is the sex of the child determined in human beings?

Accepted Answer

Human females have XX sex chromosomes and males have XY. The mother always contributes an X chromosome. The father contributes either X or Y. If the sperm carrying X fertilises the egg, the child is XX female; if the sperm carrying Y fertilises it, the child is XY male.

Question 7

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

Accepted Answer

(c) TtWW

Question 8

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?

Accepted Answer

No. The observation only shows that the trait can be inherited from parents to children. To decide whether it is dominant or recessive, we need controlled crosses or family data showing how the trait behaves in heterozygous combinations.

Question 9

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

Accepted Answer

Collect data on coat colour of many parent dogs and their puppies over several generations. Record crosses between pure-breeding parents of different colours if possible. If all F₁ offspring show one colour and the other colour reappears in later generations, the F₁ colour is likely dominant. A large sample is needed because dog coat colour can involve more than one gene.

Question 10

How is the equal genetic contribution of male and female parents ensured in the progeny?

Accepted Answer

Gametes contain only one set of chromosomes because they are formed by meiosis. During fertilisation, one male gamete and one female gamete fuse, restoring the normal chromosome number. Thus the zygote receives one set of genes from each parent.