Question

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

Answer 1

Hint: The inheritance of human skin color is an example of polygenic inheritance or multi-gene inheritance whereas the color of the flower in pea is decided by two different genes. Pea plant has contrasting traits like flower colour, stem height, seed shape, etc.

Complete answer: The human skin color shows quantitative inheritance and is controlled by three different genes. This type of inheritance pattern in which a trait or a character is controlled by more than one gene is known as polygenic inheritance. Polygenic inheritance is very complex. More than seven different allelic combinations that are heterozygous for all three genes are formed. Therefore, 64 different allelic combinations are possible. Whereas in the flower of garden pea (Pisum sativum), two genes i.e. dominant and recessive gene for violet and white color controls the inheritance pattern. Inheritance of flower color in garden pea is the example of true inheritance in which the generation shows dominant violet-colored flowers whereas in the generation both dominant and recessive traits are expressed. The human skin color is an example of polygenic inheritance in which three or more genes control the inheritance pattern of skin color. Polygenic inheritance of a character results in the formation of a bell-shaped curve.

Note: Another example of polygenic inheritance in humans is eye color that is controlled by sixteen genes. Polygenic inheritance also refers to a single inherited phenotypic trait that is controlled by more than one gene.