This gene determines the distribution of black pigment, if it is present
Breeds known to carry this mutation
Black pigment is dominant to red pigment. When black pigment is present, the bay coat colour is dominant to black.
Inheritance of the base colours of chestnut, bay and black is dependent on two genes. If MC1R is not e/e (chestnut), then the horse will show black pigment on their coat. The agouti gene (which is called ASIP) determines whether the non-chestnut horse is black or bay. The dominant allele (variant) ‘A’ limits black pigment to the points, and the horse will be bay. If the horse is homozygous for the recessive allele (a/a), the horse will be black.
Interpretation of results
a/a: Horse is homozygous for the recessive agouti allele. If the horse is not chestnut (e/e), its base colour is black.
A/a: Horse is heterozygous for the recessive agouti allele. If the horse is not chestnut (e/e), its base colour is bay.
A/A: Horse has no copies of the recessive agouti allele. If the horse is not chestnut (e/e), its base colour is bay.
Reference Reider et al. Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). Mammalian Genome 2001; 12:450-5