Phenotype: The agouti gene controls the distribution of black pigment, and determines whether a horse will have a bay or black base coat color.
Mode of Inheritance: Autosomal dominant
Alleles: A = Dominant agouti allele (responsible for bay), a = Recessive agouti allele (causes black)
Breeds appropriate for testing: All breeds
Explanation of Results:
If black pigment is present, horses with A/A genotype have black pigment restricted to the points. They will transmit the dominant agouti allele to all of their offspring.
If black pigment is present, horses with A/a genotype have black pigment restricted to the points. They will transmit the dominant agouti allele to 50% of offspring and the recessive agouti allele to 50% of offspring.
Horses with a/a genotype will have black pigment distributed uniformly over the body and will transmit the recessive agouti allele to all of their offspring.
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Agouti controls the distribution of black pigment, with two known alleles.
The mutation causing an all black phenotype is an 11 base pair deletion in exon 2 of the gene agouti-signaling protein (abbreviated as ASIP but also commonly called agouti for short). This deletion is notated as (c.191_201del). This mutation is considered to be a loss of function mutation, meaning that the recessive (a) allele causes the resulting protein to be non functional. The dominant agouti allele (A) functions normally to restrict black pigment to the points of the horse, and the recessive (a) allele is unable to restrict pigment to the points of the horse and results in a uniform distribution of black pigment across the body. Breeders interested in producing black horses need to have breeding stock carrying the a allele, in addition to the E allele of the Extension gene.
Testing for the agouti gene allows breeders to identify animals that carry or have two copies of the recessive (a) allele and can transmit this allele to produce offspring with a black base coat.
2 copies of agouti present. If present, black pigment is restricted to the points.
1 copy of agouti. If present, black pigment is restricted to the points.
If present, black pigment is distributed uniformly over the body.
Rieder, S., Taourit, S., Mariat, D., Langlois, B., & Guérin, G. (2001). Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). Mammalian Genome, 12(6), 450-455. doi: 10.1007/s003350020017