Epistasis

In inter allelic gene interaction, the gene or factor which suppresses the action of the second gene situated at another locus is called epistasis gene, and one which is suppressed is called hypostasis gene and the entire phenomenon is called epistasis.

Explanation

• White is determined by a dominant gene i.e. W. No other colour will appear in the presence of W. This W acts as epistasis to another coat colour.

• The Black colour appears only when the dominant gene for black is present along with the homozygous recessive gene w. i.e. ww.

• Homozygous recessive for both the dominant gene i.e. wwbb will produce brown.