Question

Name two human traits which show variation.

Answer 1

Hint: A genetic variation is an outcome of the presence of a variety of alleles and different types of genes in a population. The degree of variation depends upon the number of different types of alleles for the same gene.

Complete answer:
- In humans, there are a number of characteristics that exhibit variation. For example, height, skin color, blood group, eye color, etc. Some of these are multifactorial, which means they depend on other factors in addition to the genotype of the organism. For eg. Height.
- In humans, skin color is determined by the presence of melanin pigment. In humans, three pairs of genes determine the amount of melanin being synthesized. These genes are present at three different loci and a fixed amount of melanin is produced by each dominant gene. The effect of all genes is additive and the amount of melanin produced is always proportional to the number of dominant genes.
- In humans, the eye color is also determined by the amount of melanin in the eye. The concentration and location of the melanin pigment on the two-layer of the iris cause the difference in eye color. Two genes play an important role in determining eye color. One of them is responsible for the production of protein for melanin and the other one is responsible for turning on and off that protein’s production.

Note:
Inheritance such as in human skin color is referred to as polygenic/ quantitative inheritance because they are controlled by two or more than two genes. These genes are referred to as polygenes.