Agouti Gene in Dogs: Sable, Wolf Sable, Tan Points, and How It Controls Coat Color
The A locus is responsible for some of the most beautiful and complex coat patterns in dogs — but only when the K locus lets it show
The agouti gene determines how pigment is distributed within individual hairs — producing patterns that range from solid sable to wolf-gray to tan points to recessive black. It is one of the most phenotypically diverse loci in canine genetics. Understanding it is essential for breeders working with German Shepherds, Shetland Sheepdogs, Siberian Huskies, Corgis, and many other breeds where A locus variation is standard.
What Is the A Locus?
The A locus encodes ASIP — agouti signaling protein — which regulates how melanocytes switch between producing eumelanin (black/brown) and phaeomelanin (red/yellow) at different stages of hair growth.
There are four main A locus alleles in dogs, listed in order of dominance (most to least dominant):
- Ay — Sable/fawn
- aw — Wild sable/agouti
- at — Tan points
- a — Recessive black
A dog inherits one allele from each parent. The more dominant allele is expressed.
Critical caveat: The A locus is only expressed in dogs that are ky/ky at the K locus. Any dog carrying KB (dominant black) will appear solid, masking A locus expression entirely.
Ay: Sable and Fawn
Ay produces a dog where phaeomelanin predominates throughout the coat, often with dark-tipped hairs (eumelanin on the tips) creating a shaded effect. As puppies age, many sable dogs "clear" — the dark shading fades and the adult coat becomes increasingly golden or cream.
Sable appears in:
- Sable German Shepherds (the most common GSD color)
- Sable Collies (think Lassie)
- Sable Shetland Sheepdogs
- Shiba Inus (the sesame/red coloring)
- Corgis
A dog with Ay/Ay or Ay/aw or Ay/at or Ay/a will be sable — Ay dominates all other A locus alleles.
aw: Wild Sable (Agouti)
aw produces the "wolf" or wild-type agouti pattern where individual hairs are banded — dark at the tip, lighter in the middle, lighter or yellow at the base. This produces the salt-and-pepper or wolf-gray appearance.
Wild sable appears in:
- Siberian Huskies (the wolf-gray and sable colorings)
- Norwegian Elkhounds
- German Spitz
- Some German Shepherds (agouti/wolf sable variety)
- Many primitive and spitz breeds
An aw/aw dog, or aw/at or aw/a dog, expresses wild sable.
at: Tan Points
at produces the classic tan point pattern — a solid eumelanin base (black, chocolate, blue, lilac) with specific phaeomelanin (tan/gold/red) markings at defined locations: eyebrow dots, muzzle, chest, lower legs, and beneath the tail.
Tan points appear in:
- Doberman Pinschers (black and rust, red and rust)
- Rottweilers
- German Shepherd Dogs (black and tan)
- Miniature Pinschers
- English Toy Terriers
- Phantom Poodles (at/at + ky/ky)
- Dachshunds (black and tan)
A dog that is at/at will express tan points (if ky/ky). A dog that is at/a may also express tan points — at is dominant over a.
a: Recessive Black
a (recessive black) produces a solid black dog from the A locus pathway — meaning the dog is black not because of dominant black (KB) but because its ASIP is nonfunctional, preventing phaeomelanin production anywhere in the coat.
Recessive black appears in:
- Some German Shepherds (solid black GSDs are often a/a)
- Belgian Malinois and Belgian Sheepdogs
- Shetland Sheepdogs
- Schipperkes
A dog must be a/a to be recessive black — it requires two copies since all other A alleles dominate a.
A Locus and K Locus Interaction
The most important thing to remember about the A locus is that it only matters if the dog is ky/ky. Dogs with even one KB allele will appear solid-colored, with no A locus expression visible.
This creates hidden carriers of every A locus allele. A KB/ky dog that is Ay/at will look solid black or solid-colored — but bred to a ky/ky partner, its offspring may be sable, tan point, or a mix.
This interaction explains many "unexpected" litter colors in GSD, Sheltie, and Corgi breeding programs where dominant black lines exist alongside patterned lines.
Predicting A Locus Outcomes
| Parent 1 A Locus | Parent 2 A Locus | Possible Offspring |
|---|---|---|
| Ay/at | Ay/at | Ay/Ay, Ay/at, at/at (sable or tan point) |
| at/at | at/a | at/at or at/a (all tan point) |
| at/a | at/a | at/at, at/a, a/a (tan point or recessive black) |
| Ay/aw | aw/at | Ay/aw, Ay/at, aw/aw, aw/at |
Summary
The A locus produces sable (Ay), wild agouti (aw), tan points (at), and recessive black (a), in that order of dominance. The specific pattern a dog expresses depends on which two A locus alleles it inherits and whether the K locus allows A locus expression at all. DNA testing for A locus combined with K locus testing gives breeders accurate predictions of litter color outcomes in breeds where A locus variation is common.