Question

In pea plants, the colour of the flower is either violet or white whereas human skin colour shows many gradations. Explain giving reasons how it is possible.

Answer 1

In pea plants, the colour of the flower is either violet or white because the trait follows the law of dominance where violet is dominant and white is recessive. As a result, only two distinct phenotypes appear,either the dominant violet or the recessive white. This is a simple case of Mendelian inheritance controlled by a single gene with two alleles.

In contrast, human skin colour shows many gradations because it is a quantitative character controlled by multiple genes, a phenomenon known as polygenic inheritance. Each gene contributes to the skin colour, and their combined effect results in a continuous range of variations rather than distinct categories.

Thus, the dichotomy in flower colour results from single-gene control with dominance, while the gradation in human skin colour arises from multiple genes interacting together to produce a spectrum of phenotypes.