Which gene is responsible for lightening bay to buckskin and chestnut to palomino?

The gene responsible for lightening bay to buckskin and chestnut to palomino is the dilute gene. This gene affects the pigmentation of a horse's coat by diluting the base color. Specifically, when a bay horse possesses the dilute gene, it will soften the rich reddish-brown of the coat to create the creamy tan of a buckskin. Similarly, in chestnut horses, the presence of the dilute gene lightens the deep red tones to produce the golden hue characteristic of palomino horses.

This genetic mechanism is an essential aspect of equine coloration genetics, as it directly contributes to the variety of coat colors observed in horses. The black gene influences the production of black coats but does not cause dilution. The agouti gene is involved in determining whether a black coat will be modified to bay or remain black. The roan gene, on the other hand, affects the distribution of white hairs in a coat, creating a roan pattern but does not cause the dilution seen with the dilute gene. Understanding these genetic influences is crucial for evaluating and predicting horse coat colors in breeding and evaluation contexts.