Which type of inheritance is responsible for skin colour in human bei…

The correct answer is Option (2) → Polygenic inheritance

Some traits do not fall into two clear classes but show a whole range, like human height. Such traits are controlled by three or more genes, and the effect of each allele adds to the others; the environment also has a say. This is polygenic inheritance, and human skin colour is a classic example.

Option (1) Co-dominance — Incorrect. In co-dominance both alleles of one gene express together in the heterozygote, as with I^A and I^B in blood group AB. Skin colour is controlled by several genes, not one.

Option (2) Polygenic inheritance — Correct. Skin colour is controlled by several genes (A, B, C in the NCERT example) whose alleles add up, so all shades from darkest to lightest occur.

Option (3) Pleiotropy — Incorrect. Pleiotropy is the opposite situation: a single gene has several phenotypic effects, as in phenylketonuria. Skin colour is one trait controlled by many genes.

NCERT Extract:
Polygenic Inheritance – “… Such traits are generally controlled by three or more genes and are thus called as polygenic traits. Besides the involvement of multiple genes polygenic inheritance also takes into account the influence of environment. Human skin colour is another classic example for this. In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive.”