Testing Summary
The Co Locus (Cocoa) coat color test reliably determines if a dog has one of the following genotypes at the Co Locus:
| CO/CO | This dog does not carry any copies of the co (cocoa) Mutation and has a Co Locus genotype of CO/CO. 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 including the B Locus (Brown). This dog will pass one copy of CO to 100% of its offspring and cannot produce co/co (cocoa) dogs. Interpretation: Black coat, nose and foot pads (does not carry cocoa) |
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| CO/co | This dog carries one copy of the co (cocoa) mutation and has a Co Locus genotype of CO/co. 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 including the B Locus (Brown). This dog will pass one copy of CO to 50% of its offspring and one copy of co (cocoa) to 50% of its offspring. This dog can produce co/co (cocoa) offspring if bred to a dog that is also a Carrier of co (cocoa) (CO/co or co/co). Interpretation: Black coat, nose and foot pads (carries one copy of cocoa) |
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| co/co | This dog carries two copies of the co (cocoa) mutation and has a Co Locus genotype of co/co. Thus, this dog typically will have a cocoa colored coat, nose and foot pads. Depending on the breed, co/co dogs may be referred to as cocoa, brown or chocolate. However, this dog’s coat color is dependent on the genotypes of many other genes. This dog will pass one copy of co to 100% of its offspring. This dog can produce co/co (cocoa) offspring if bred to a dog that is also a carrier of co (CO/co or co/co). Interpretation: Cocoa coat, nose and foot pads (carries two copies of cocoa) |
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Detailed Summary
Mutations of the HPS3 gene (Co Locus) impact canine coat color by partially disrupting regular eumelanin (black pigment) synthesis resulting in brown pigment which, depending on the breed, may be referred to as cocoa, brown or chocolate. HPS3 is in the same genetic pathway as the TYRP1 gene (B Locus) which also plays a role in eumelanin synthesis. Mutations in the TYRP1 gene result in brown pigment as well and, depending on the breed, may be referred to as brown, red, liver or chocolate. Mutations at the Co Locus produce a slightly darker brown than that produced by mutations in the B Locus. In addition, cocoa pups often have blue eyes and coats that darken over time.
Mutations of the HPS3 and TYRP1 gene result in brown pigment being produced in the coat, nose and footpads of dogs 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. 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 co may produce cocoa (or brown or chocolate dogs, depending on the breed) if bred to a dog that is also a Carrier of the co Mutation (CO/co or co/co).
Disease Association Note: Mutation of the HPS3 gene in humans is associated with Hermansky-Pudlak syndrome type 3, a bleeding disorder that is also associated with visual impairments. Further studies are needed to determine if cocoa-colored dogs have any clinical issues associated with this mutation.
Testing Tips
Genetic testing of the HPS3 gene will reliably determine whether a dog is a genetic Carrier of cocoa coat color. Cocoa coat color is known to be inherited in an Autosomal Recessive manner in dogs meaning that dogs need to inherit two copies of the co Allele to have a cocoa colored coat. Each pup that is born to a dog with cocoa coat color has a 100% chance of inheriting one copy of the co allele from that parent. To produce cocoa pups, both the dam and the sire must be at least carriers of one copy of the co allele (CO/co or co/co). However, the dog’s coat color is also dependent on the dog’s genotypes at the E, K, A, and B genes among others. Reliable genetic testing is important for determining breeding practices. NOTE: Not all of the genetic mutations that result in a brown coat color are known.
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
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Kiener S, Kehl A, Loechel R, Langbein-Detsch I, Muller E, Bannasch D, Jagannathan V, Leeb T. Novel bron coat color (cocoa) in French bulldogs results from a nonsense variant in HPS3. 2020 Jun; 11(6):636.
[PubMed: 32526956]
