Cocoa Locus (CO-LOCUS)
Chocolate, Cocoa, French Bulldog Brown
Cocoa Locus (CO-LOCUS) is a mutation that leads to brown/chocolate coat color in French Bulldogs previously known as “non-testable chocolate”. There are several known mutations in the TYRP1 gene (B-LOCUS) that can lead to a brown/chocolate coat color in dogs. Even though these mutations account for the brown/chocolate coat color in most dogs, a brown/chocolate coat color in French bulldogs can be due to an additional unique mutation located in the HPS3 gene. This coat color is referred to as “Cocoa” and can be visibly darker brown than the coat color seen in dogs with the typical TYRP1 mutations. The CO-LOCUS mutation can have a complex inheritance in combination with the B-LOCUS mutations that are still being studied. It is currently believed that one copy of the CO-LOCUS mutation and one copy of the B-LOCUS mutation will not result in a brown phenotype. It is not currently possible to predict the coat color of a dog that inherits two copies of both the CO-LOCUS and B-LOCUS mutations. The difference in coat color between the CO-LOCUS and B-LOCUS mutations is subtle with the “Cocoa” color having a slightly darker color than the more common brown/chocolate.
Reading Your Results
These dogs have two copies of the normal gene and will neither develop a cocoa colored coat nor pass this mutation to their offspring.
B. (CARRIER/NOT AFFECTED):
These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They will not develop a cocoa colored coat but will, if bred, pass the mutation to 50% of its offspring, on average.
C. (AT RISK/AFFECTED):
These dogs have two copies of the mutation associated with cocoa coat color which results in a cocoa colored coat dependent on other coat color loci.
Kiener S, Kehl A, Loechel R, Langbein-Detsch I, Muller E, Bannasch D, Jagannathan V, Leeb T. Novel brown coat color (cocoa) in French bulldogs results from a nonsense variant in HPS3. 2020 Jun; 11(6):636. [PubMed: 32526956]