Notation: A
Alleles: A, A+, At, a
Dominance: A+ > A > At > a
Basic Function: Restricts where black pigment is produced on the body. For Agouti to be expressed, the horse needs to be able to make black pigment, so it must have either EE or Ee at the extention locus.
Genotypes & Phenotypes:
* = any allele.
E*/aa = Black
E*/Ata or E*/AtAt = Seal Bay
E*/Aa or E*/AA or E*/AAt = Classic Bay
E*/A+* = Wild Bay
ee/A+* or ee/A* or ee/At* = Chestnut
Description:
- When a A, At or A+ is present, it "turns off" black pigment in certain areas of the body.
In A, classic bay, the body is mostly brown/red, with black legs.
In At, seal bay/brown, most of the body is black, with brown only on the soft areas of the body, such as the belly, flank and often around the nose and eyes.
In A+, wild bay, only the very lowest areas of the legs are black, around the pasterns. There may be a small amount of black on the knees and hocks.
The mane and tail are black, and the hooves and skin grey in all variations.
This gene requires black pigment to be present to show, so it will not affect chestnut coats.
- -Some wild bay horses may have a lighter body colour than classic bay.
-There is some evidence that wild bay might be recessive to classic bay, or that it may be caused by a completely different gene acting with agouti, but for now I'm including it here as the most dominant agouti allele.
Genetic Cause:
- See basic Mammalian Colour Genetics, Agouti.
