03-17-2013, 02:10 AM
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Modifying black: Agouti (bay, brown, or solid) |
We've only discussed one LOCUS (spot where a pair of genes exists) on the horse's chromosome, so far: the E/e locus. Now we move on to another one, the AGOUTI locus, which contains a pair of genes that only affect black pigment.
This means that if a horse has only red pigment (is "ee" at the red/black locus), the genes at the agouti locus have no effect on that horse's color.
If the horse DOES have an "E" gene, meaning it does have black pigment, the agouti genes affect it as follows:
A, or the BAY AGOUTI gene, when present on a horse with an E (black pigment) gene, will limit the black pigment to the points (mane, tail, lower legs) of the horse. A/bay is the "most dominant" of the agouti genes, and will always be active when it's present.
At, or the BROWN AGOUTI gene, when present and active (no A gene) on a horse with an E (black pigment) gene, will allow the black pigment to spread over most of the body, but restrict it on the muzzle and underbelly, etc., causing those areas to be a tan color. At/brown is the "second most dominant" of the agouti genes, and will be active if no A/bay gene is present