When multiple genes affect or modify a trait, these are known as polygenes.

For example, at least two different genes are suspected of influencing the silver and golden coat colours found in many cat breeds. Interactions with other genes, and polygenes modify the effect. A dominant silver inhibitor gene is known to exist but the mutation causing it has not yet been identified The dominant Silver (Inhibitor (I,i) reduces or eliminates phaeomelanin (yellow pigment) production in the cat’s hair. On agouti hairs there are dark bands, but the light bands are changed from yellowish to white.

Wide-band (Wb) affects the length of the bands on agouti hairs. It’s more accurate to call it an effect rather than a gene. It is very variable, causing many short bands or fewer longer bands. Breeders have selected for fewer longer bands. Cats with fewer longer bands appear as chinchillas in silver cats and as goldens in non-silver cats. The wide-band effect is recessive. Several mutations of the CORIN gene cause wide-band effects in different breeds. Variable Wb effects may be due to multiple genes at different loci (positions on chromosomes) as shown below.

Where multiple genes cause similar traits there can be unexpected results if the cats are bred together. One example is the interaction of Sphynx Hairless gene (recessive) and Donskoy Hairless gene (incomplete dominant).