DNA test for the Agouti gene that controls distribution of black pigment throughout the coat.
This test does not determine if a horse is homozygous for black factor. To determine black homozygosity is necessary to test for red/black Factor (Extension gene)
- 30 to 40 - hair roots - envelope
- 5 mL - blood - K3 EDTA tube
- 2 to 5 working days
- Agouti is not shown physically on red (e/e) horses. Therefore, a breeder might want to test a chestnut base horse to see if it is an Agouti carrier.
- Testing bay horses might be desired to see whether the horse carries one (A/a) or two (A/A) copies of the Agouti allele. A homozygous Agouti (A/A) horse will always pass Agouti to its offspring whereas a heterozygous (A/a) horse will have a 50% chance of passing on the gene.
- Another reason to test for Agouti might be if there is some doubt whether a black horse is truly black or a very dark bay. The effects of other genes might also make it hard to tell if Agouti is present or not.
- A/A - Bay or Brown - Dominant Homozygous for Agouti. Black pigment restricted to the points. The horse cannot have black foals regardless of the coat color of the mate. The basic coat color will be bay or brown in the absence of other color modifying genes.
- A/a - Bay or Brown - Heterozygous for Agouti. Black pigment distributed in point pattern. The horse can transmit either (A) or (a) allele to its offspring. The basic coat color will be bay or brown unless modified by other coat color modifying genes.
- a/a - Black - Recessive homozygous for Agouti. Black pigment distributed uniformly. The basic coat color will be black in the absence of other coat color modifying genes.
The Agouti gene controls the distribution of black pigment. This pigment can be either uniformly distributed or distributed to “points” of the body (ear rims, lower legs, mane, tail).
Agouti has been linked to a deletion of 11 nucleotides in the agouti gene. The 11 nucleotide deletion of this gene is the recessive form of the gene.
Only when the agouti gene is homozygous for the deletion (aa) is the black pigment evenly distributed.
Heterozygous (A/a) or homozygous for the absence of the 11 nucleotide deletion (A/A) results in point distribution of black pigment.
Agouti has no effect on homozygous positive red factor (ee) horses as there has to be black pigment present for agouti to have an effect.