Genetics
The Agouti (A) Locus: Wolf Sable, Tan Points, and Dog Color Patterns
The A (agouti) locus is responsible for sable, wolf gray, tan points, and solid recessive black — the most diverse set of color patterns controlled by a single locus in dogs.
April 1, 2024 · 6 min read
The A Locus Alleles (Dominance Order)
- Ay (Fawn/Sable): Most dominant. Produces fawn to sable coloring — ranges from clear fawn (one solid color) to heavily sabled (dark-tipped individual hairs creating a wolf-like shading).
- aw (Wolf Agouti): Produces the banded hair pattern seen in German Shepherds, wolves, and huskies — individual hairs alternate between eumelanin and phaeomelanin bands.
- at (Tan Points): Produces tan markings on specific body locations — eyebrows, cheeks, chest, legs, and under tail. Creates the 'phantom' pattern in Poodles and Doberman-style markings.
- a (Solid Recessive Black): Most recessive. Both copies (a/a) produce solid black eumelanin with no pattern expression.
The A Locus Only Matters If K Locus Allows It
The A locus patterns are only visible in dogs that are ky/ky at the K locus. Dogs that carry KB (dominant black) will have their A locus patterns completely masked — they will appear solid (or appropriate E locus color) regardless of their A locus genotype. This is a crucial concept for understanding why solid-colored dogs can produce patterned offspring.
Sable in Cavapoos and Poodles
Sable (Ay) is common in some Poodle and Cavalier lines. A sable puppy is often born very dark — appearing almost black — because the eumelanin tip of each banded hair dominates in new coat. As the puppy grows and coat is groomed, the phaeomelanin base becomes visible and the dog can lighten dramatically. Adult sable Poodles often appear a warm brown or dusty gold — a complete transformation from their puppy appearance.