| Other Names: | B locus, ba, bc, bd and bs loci |
|---|---|
| Affected Genes: | TYRP1 |
| Inheritance: | Autosomal Recessive |
| Mutation(s): | ba = T>G, Chr11:33319349 (Australian Shepherd Type), bc = T>A, Chr11:33317810, bd = 3 bp deletion (del CCT), Chr11:33326727-33326729, bs = C>T, Chr11:33326685 |
| Breed(s): | All Breeds |
Testing Summary
The B Locus (Brown) coat color test reliably determines if a dog has one of the following genotypes at the B locus:
| B/B | This dog does not carry any copies of the ba, bc, bd or bs mutations and has a B locus genotype of B/B. Thus, this dog typically will have a black coat, nose, and foot pads. However, this dog’s coat color is dependent on the genotypes of many other genes. This dog will pass one copy of B to 100% of its offspring and cannot produce b/b dogs. Interpretation: Black coat, nose and foot pads (does not carry brown) |
|---|---|
| B/b | This dog carries one copy of one of the b mutations and has a B locus genotype of B/b. Thus, this dog typically will have a black coat, nose, and foot pads. However, this dog’s coat color is dependent on the genotypes of many other genes. This dog will pass one copy of B to 50% of its offspring and one copy of b to 50% of its offspring. This dog can produce b/b offspring if bred to a dog that is also a Carrier of a b Mutation (B/b or b/b). Depending on the breed, b/b dogs may be referred to as brown, chocolate, liver or red. Interpretation: Black coat, nose and foot pads (carries one copy of brown) |
| b/b | This dog carries two copies of one of the b mutations and has a B locus genotype of b/b. Thus, this dog typically will have a brown coat, nose and foot pads. Depending on the breed, b/b dogs may be referred to as brown, chocolate, liver or red. However, this dog’s coat color is dependent on the genotypes of many other genes. This dog will pass one copy of b to 100% of its offspring. This dog can produce b/b offspring if bred to a dog that is also a carrier of a b mutation (B/b or b/b). Interpretation: Brown coat, nose and foot pads (carries two copies of brown) |
| B/b or b/b | This dog carries one or more copies of the four possible b mutations and has a B locus genotype of B/b or b/b that cannot be distinguished without additional testing of parental samples or by examining the coat, nose and footpad color of the dog. Dogs inherit two copies of the B locus, one from each parent. Because there are four different B locus mutations that can potentially be identified, as well as some limitations inherent to genetic testing methodologies currently available, a result of “B/b or b/b” means that it cannot be determined if the b mutations identified in this dog are present on the same copy of the B locus inherited from one parent or if they occur on separate copies of the B locus inherited from each of the parents. If the mutations identified are all present on the same copy of the B locus, this dog will have a B/b genotype and typically will have a black coat, nose and footpads. If the mutations identified are present on different copies of the B locus, this dog will have a b/b genotype and may have a brown coat, and will typically have a brown nose and footpads. Depending on the breed, b/b dogs may be referred to as brown, chocolate, liver or red. However, this dog’s coat color is dependent on the genotypes of many other genes. The B locus genotype for this dog can be inferred without the need for parental testing by evaluating the color of this dog’s nose. If this dog’s nose is brown, the B locus genotype of this dog must be b/b and this dog will pass one copy of b to 100% of its offspring. If this dog’s nose is black, the final B locus genotype of this dog must be B/b and this dog will pass one copy of B to 50% of its offspring and one copy of b to 50% of its offspring. In either case, this dog carries at least one copy of b and can produce b/b offspring if bred to a dog that is also a carrier of a b mutation (B/b or b/b). Interpretation: Black or brown coat, nose and foot pads (carries at least one copy of brown) |
Detailed Summary
Mutations of the TYRP1 gene at the brown (B) Locus impact canine coat color by disrupting regular eumelanin (black pigment) synthesis which causes the appearance of black pigmented areas to be brown, which, depending on the breed, may also be referred to as red, chocolate or liver. The B locus also controls the color of the dog’s nose and foot pads regardless of the dog’s genotype at the E locus because eumelanin is still produced in the epidermis of the nose and foot pads of e/e dogs. The B locus genotype for a dog is determined by the combination of the genotypes identified at the ba, bc, bd, and bs loci. Because dogs inherit two copies of the B locus (one copy from each parent), the ba, bc, bd, and bs mutations confer brown coat, nose, and foot pads when at least one of these DNA mutations is present on both copies of the B locus in the dog. If the dog has one or no copies of b then the dog typically will have a black coat, nose, and foot pads. However, the dog’s coat color is also dependent on the E, K, and A genes among others. Dogs that have one or two copies of b may produce brown (or red, chocolate or liver dogs, depending on the breed) if bred to a dog that is also a Carrier of a b Mutation (B/b or b/b). NOTE: Not all of the genetic mutations that result in a brown coat color are known. However, the mutation for brown (also known as “cocoa”) in the French bulldog has been identified recently but is not included in this test.
Testing Tips
The Paw Print Genetics’ B Locus (Brown) coat color panel tests four brown loci (ba, bc, bd, and bs) and includes the recently identified brown/red Mutation found in Australian Shepherds and related breeds. The brown (B) locus interacts closely with the E, K, and A genes to produce the dog’s coat color. Because of the combined interaction of the four brown loci, non-brown dogs can be carriers of brown genes that produce brown (or red, chocolate or liver depending on the breed) puppies. Genetic testing of all four brown loci will accurately determine whether a dog is a genetic Carrier of brown coat and nose color. Note: In situations where two or more single copy mutations of ba, bc, bd, and bs are identified in a dog, the presence of multiple mutations being located on a single copy of the B locus cannot be excluded. Therefore, the overall B locus genotype for a dog could be B/b or b/b and cannot be determined without additional testing of parental samples. However, the B locus genotype for a dog in this situation can be inferred without the need for parental testing by evaluating the color of the dog’s nose (see B/b or b/b genotype interpretation above).
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
- Hrckova Turnova E, Majchrakova Z, Bielikova M, Soltys K, Turna J, Dudas A. A novel mutation in the TYRP1 gene associated with brown coat color in the Australian Shepherd Dog Breed. Anim Genet. 2017 Oct; 48(5):626. [PubMed: 28497851]
- Schmutz SM, Berryere TG, Goldfinch AD. TYRP1 and MC1R genotypes and their effects on coat color in dogs. Mamm Genome. 2002 Jul; 13(7):380-7. [PubMed: 12140685]
