The Hermansky-Pudlak syndrome 3 (HPS3) gene, also known as cocoa coat colour or co-locus is responsible for the brown colour in French Bulldogs. Mutations of the HPS3 gene interfere with the eumalin (black pigment) synthesis, which results in brown-pigmentation. The brown colour caused by the HPS3-variants is known to darken over age and to be slightly darker in adults that the brown colour caused by the TYRP1-related variants (B-locus). The co-locus is recessive and therefore needs two copies of the gene to present the phenotype. This co-locus can be present in French Bulldogs with various coat colours; brown, lilac, black, blue, cream, fawn or white, but the phenotype might be less visible in some cases. The complete phenotype of the coat, footpads and nose also depends on the A-, E-, K- and B-locus genes. Right now, no interaction in French Bulldogs between the co- and B-locus have been reported. Therefore it is not possible to predict what phenotype the combination of these variants would cause.
N/N = cocoa variant not present. The cocoa phenotype is not expressed, the offspring won’t inherit a copy of the co-locus.
N/co = carrier of the cocoa variant. Phenotype is not present. 50% of the offspring will inherit one copy of the co-locus.
co/co = the cocoa phenotype is present. The display of this phenotype depends on the interaction between other colour genes (loci). 100% of the offspring will get one copy of the co-locus.
