Over dominance is a form of non-additive gene interaction where heterozygous individuals exhibit superior traits compared to either homozygous genotype. It is exemplified in rabbits where the A1A2 genotype produces antigen 3 in addition to antigens 1 and 2. Epistasis is another form of non-additive gene interaction that involves two or more pairs of non-allelic genes interacting. In horses, coat color is determined by epistasis between genes for black (B) vs chestnut (b) color and a dominant white (W) gene, which inhibits the expression of B and b.