Coat colour A locus / Agouti (ASIP-related) - Dog

What does this test examine?

This DNA test examines the ASIP gene, better known as the A locus or Agouti locus, in dogs. The A locus helps determine how dark eumelanin and lighter phaeomelanin are distributed across hairs and body regions. It is therefore central to patterns such as fawn/sable, wild sable, tan points, black-and-tan, tricolour and recessive black.

What does the A locus mean for the coat?

The A locus works as a dominance hierarchy. In classic market terminology the alleles are often described as Ay, aw, at and a. Ay is mainly associated with fawn or sable, aw with wild sable or wildtype agouti, at with tan points or black-and-tan, and a with recessive black when two copies are present. More recent literature describes the same region using ASIP promoter haplotypes such as dominant yellow, shaded yellow, agouti, black saddle and black back.

The final coat colour also depends strongly on other coat-colour genes. The K locus can mask A-locus patterns, while the E locus determines whether dark pigment can be expressed in the coat. This makes the test useful even when the pattern is not fully visible.

Inheritance and result

The A locus behaves as an allelic series: a more dominant allele can hide the effect of a more recessive allele. A dog can therefore show a dominant pattern while still carrying a recessive pattern for offspring.

• Ay is usually associated with fawn or sable.
• aw is associated with wild sable or wildtype agouti.
• at is associated with tan points, black-and-tan and tricolour.
• a causes recessive black when two copies are present.

Practical value of this test

For breeders, A-locus testing is valuable because it reveals hidden alleles before matings are planned. The result helps predict coat-colour expectations more realistically, reduce surprises in litters and plan combinations for sable, wildtype agouti, tan points or recessive black.

• Helps explain why a dog shows or carries a specific pattern.
• Supports colour planning together with E, K, B and D locus results.
• Shows which A-locus alleles can be passed to offspring.
• Useful for buying, selling, litter planning and building reliable colour information within a line.