Lokus A (Agouti) - bay/black

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

Allele A of gene ASIP controls spreading of eumelanin on horse bodies. The dominant allele A limits spreading of black colour to the mane, tail and lower legs. The recessive allele a and if in homozygote condition aa does not limit spreading of the black colour on the body. Therefore recessive homozygote horses (aa) have black colour all over their bodies and they are black horses. There are probably several other alleles (3 to 4) in this locus A. In the order of diminishing dominance, they are as follows: A+ > A > At > a. Allele A+ is responsible for wild colouring of horses similar to protective coloration of most of wild animals (e.g., Przewalski’s horse). The remaining 3 alleles modify black colour in the following way:

• allele A limits occurrence of black only to the mane, tail and lower legs

• allele A^t (in genotypes A^tA^t and A^ta) does not limit black as much as allele A; however, black is lightened to dark bay, the lightening is present in particular on shoulder blades and flanks

• allele a in homozygote condition is responsible for black colour distributed all over the horse body

Genomia Laboratory determines allele a – recessive black colouring. Allele A and At are not differentiated by the test.