Tan Point Genetics in Dogs: The At Allele Explained
The classic black-and-tan or tricolour pattern seen in Dobermans, Rottweilers, German Shepherds, Corgis, and dozens of other breeds is controlled by a single genetic locus — the A locus. Here is how it works.
Tan point colouring — the signature dark body with warm tan markings on the cheeks, eyebrows, chest, legs, and under the tail — is one of the most recognisable coat patterns in dogs. It is produced by the at (tan point) allele at the agouti signalling protein (ASIP) gene locus, known as the A locus.
The A Locus — The Agouti Hierarchy
The A locus controls where black and yellow/tan pigment are distributed in the coat. There are several alleles, arranged in a hierarchy of dominance:
| Allele | Name | Effect |
|---|---|---|
| Ay | Sable/Fawn | Yellow/red throughout; dominant |
| aw | Wolf sable/Agouti | Banded hairs (wolf grey); intermediate |
| at | Tan point | Dark body, tan markings on points |
| a | Recessive black | Solid black/brown; recessive |
Tan point (at) is recessive to sable and agouti. A dog needs two copies of at to express the tan point pattern — unless the dog has no dominant alleles above it.
How at Works
A dog expressing tan point colouring (at/at) has black or brown (chocolate) pigment on the body and yellow/red (tan, mahogany) pigment restricted to the "points" — specific locations determined by the pattern:
- Above each eye (eyebrow spots)
- On the cheeks and muzzle
- On the chest (often two spots or a V)
- On the inner sides of all four legs
- Under the tail
- On the toes
The exact shade of tan ranges from cream to deep rust, influenced by other loci (particularly the E locus for intensity and the B locus for liver modifier).
Tan Point in Common Breeds
Doberman Pinscher: Almost all Dobermans are at/at with black (B) or red (bb) base. The classic black-and-rust or red-and-rust are both tan point.
Rottweiler: At/at with black base. The mahogany tan markings are characteristic.
German Shepherd: At/at is the saddle pattern's foundation. Most black-and-tan GSDs carry at.
Pembroke Welsh Corgi: Tricolour Corgis are at/at. Red-and-white Corgis are Ay/Ay or Ay/at.
Australian Shepherd: Tricolour Aussies (black/red tricolour) are at/at or at/a.
Miniature Pinscher: at/at with black or chocolate base.
Dachshund: Black and tan Dachshunds are at/at.
Carrying vs Expressing at
A dog can carry one copy of at without expressing tan point:
- Ay/at: Sable dog that carries tan point — all puppies from this dog × at/at will be either sable-carrying-at or full tan point
- aw/at: Agouti/wolf grey dog that carries tan point
DNA testing reveals at carrier status, which is invisible visually in dogs with a dominant allele.
Breeding for Tan Point
To produce tan point offspring (at/at), at least one parent must carry two copies of at, or both parents must carry at least one copy.
Example: Ay/at (sable carrying at) × at/at (tan point) = 50% Ay/at (sable carrying at), 50% at/at (tan point).
Example: at/at × at/at = 100% at/at (all tan point).
Interaction with Other Loci
Tan point expression is modified by other loci:
- B locus: bb (chocolate/liver) changes black base to brown → chocolate-and-tan instead of black-and-tan
- D locus: dd (dilute) changes black to blue, tan to lighter cream → blue-and-tan in some breeds
- E locus: ee (recessive red) masks tan point entirely — a dog cannot express tan point if it is ee
- K locus: KB (dominant black) masks tan point — a KB dog with at/at will be solid black, not tan point
Understanding the interaction between A locus, B locus, D locus, E locus, and K locus is essential for predicting tan point outcomes in complex breeding programmes.
Summary
Tan point colouring is controlled by the at allele at the A locus — recessive, requiring two copies for expression (unless no dominant allele is present). It produces the classic dark body with tan markings at specific points. Interaction with B, D, E, and K loci modifies the final colour. DNA testing at the A locus reveals carrier status in dogs that visually appear sable, agouti, or solid.