Locus E - red factor

(Review article about horse coat color genetics is available here Horse coat colors.)

Dominant allele E (genotypes EE or Ee) of MCR1 gene allows creation of eumelanin while the recessive allele e prevents formation of eumelanin. Genotype ee (recessive homozygote) is responsible for black colouring and allows formation of phaeomelanin. The black hair pigment of horses may spread all over the body – the so-called black horse. In the case of only partial spreading of black to the mane, tail and lower legs, the horse is considered bay. Full or partial spreading of black colour on the body is affected by epistatic (superior) effects of another gene A (agouti). Phenotypes EE and Ee are responsible for black, dark bay and bay colours. ee phenotype is responsible for various shades from dark roan to light roan.