1How do Mendel's experiments show that traits may be dominant or recessive?
Answer & Reference:
Mendel crossed pure tall (TT) and short (tt) pea plants. All F₁ progeny were tall, showing that tallness is dominant. When F₁ plants were self-pollinated, F₂ showed a 3:1 ratio—3 tall : 1 short—proving that shortness was inherited but not expressed in F₁, hence recessive. (Section 8.2.2)
2How do Mendel's experiments show that traits are inherited independently?
Answer & Reference:
Mendel crossed pea plants with two traits—e.g., tall with round seeds and short with wrinkled seeds. F₁ were all tall with round seeds. In F₂, new combinations appeared—tall with wrinkled and short with round seeds—showing that seed shape and plant height are inherited independently. (Section 8.2.2, Fig. 8.5)
3A 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?
Answer & Reference:
Yes. Since the daughter has blood group O, she must have received an O allele from each parent. The man (blood group A) must carry one O allele (genotype AO), meaning blood group A is dominant over O. If O were dominant, the daughter could not be O when the father is A. (Inferred from principles in Section 8.2.2)
4How is the sex of the child determined in human beings?
Answer & Reference:
Human females have XX sex chromosomes; males have XY. All children inherit an X chromosome from the mother. The father contributes either X (girl) or Y (boy). Thus, the sex of the child is determined by the paternal chromosome. (Section 8.2.4, Fig. 8.6)
5A 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 & Reference: (c) TtWW
Explanation: All progeny had violet flowers → violet (W) is dominant and tall parent must be WW. Half progeny were short → tall parent must be heterozygous for height (Tt). Hence, genotype = TtWW. (Based on Section 8.2.2)
6A 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 & Reference:
This suggests that light eye colour is likely recessive. If it were dominant, even one parent with light eyes could produce children with dark eyes (if the other parent had recessive alleles). But since light-eyed children usually have light-eyed parents, it implies both parents must carry the recessive allele, supporting recessiveness. (Inferred from Section 8.2.2)
7Outline a project which aims to find the dominant coat colour in dogs.
Answer & Reference:
1. Select two purebred dogs—one with black coat, one with brown.
2. Mate them and observe F₁ coat colour.
3. If all F₁ are black → black is dominant.
4. Self-cross F₁ or cross F₁ siblings to get F₂.
5. If F₂ shows ~3:1 ratio (black:brown), confirms dominance of black. (Based on Mendel’s method in Section 8.2.2)
8How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer & Reference:
During gamete formation, meiosis reduces the chromosome number by half. Each germ cell (sperm or egg) carries one set of chromosomes. At fertilization, sperm and egg fuse to restore the full chromosome number—half from each parent—ensuring equal genetic contribution. (Section 8.2.3)
Figure 8.6: Sex determination in human beings (Simplified SVG representation)
Figure 8.5: Independent inheritance of two traits (seed shape and colour)
T1Phenotypic ratio in dihybrid cross (F₂ generation)
Reference: Based on data in Figure 8.5 (Page not numbered, but in Section 8.2.2)