Question

Explain epistasis with the help of an example.

Answer 1

Epistasis is a gene interaction in which one gene masks or modifies the expression of another non-allelic gene.

For example, in mice, coat colour is controlled by two genes. Gene C is necessary for colour formation, while gene A determines agouti or black colour. The genotype cc prevents pigment formation and produces albino mice, regardless of the allele present at the A locus.

Thus, cc is epistatic to the A gene, producing an F₂ phenotypic ratio of 9 agouti : 3 black : 4 albino.