Question

Name two human traits which show variations.

Answer 1

Hint: Character is described as the feature of an individual and distinguishable feature of a character and its detectable variant is known as trait. For example height is a character of an organism and whether an organism is tall or dwarf is its trait.

Complete answer:
The two human traits that show variation are skin colour and eye colour of humans as they are polygenic traits.
The traits which are controlled by two or more than two genes are called polygenic traits. The inheritance or passing of polygenic traits is called polygenic or quantitative inheritance.
The presence of melanin pigment is the only reason that determines the skin colour. The amount of melanin developing in the individual is determined by three (two also) pairs of genes. These kinds of genes of skin colour are present mainly at three different loci and each dominant gene is responsible for the synthesis of fixed and certain amounts of melanin only.
The effect of all the genes is additive that is show addition and combination and the amount of melanin produced is always proportional to the number of dominant genes present in an individual. Subsequent studies after Davenport have shown that as many as six genes may be involved in controlling the skin colour in human beings.
The frequency distribution for skin colour can be represented either as a histogram or in the form of a bell shaped normal distribution curve.
H. Nilsson-Ehle (1908) and East (1910) demonstrated segregation and assortment of genes controlling quantitative traits, e.g., Kernel colour in wheat and corolla length in tobacco.


Note: In quantitative inheritance or polygenic inheritance, the dominant alleles have cumulative effect, with each dominant allele expressing a part of functional polypeptide and full trait is shown when all the dominant alleles are present. Genes involved in quantitative inheritance are called polygenes.