Epistasis Analysis

A contrary relationship between two genes is epistasis, where one gene masks or alters the expression of another. The influencing gene is said to be epistatic to the gene being masked.

For example, a gene that codes for tyrosinase-related protein 1, or TYRP1, determines the coat color of dogs —  black or brown.

Another gene, Tyr, codes for the enzyme tyrosinase, which is responsible for pigmentation in animals. A mutation in this gene can cause the absence of pigment, resulting in an albino dog which lacks any coloration.

The order in which these two genes are expressed can be determined by an epistasis test.

If a mutation in the Tyr gene produces an albino dog that still has the wild-type TYRP1 gene, it can be concluded that the Tyr gene masks the effect of the TYRP1 gene. This would mean that Tyr is epistatic to TYRP1.