Cocoa

Description

Variants in the TYRP1 gene, or B locus, are the most common cause of brown, chocolate or liver coat color.  There are currently a total of five known TYRP1 gene mutations that impact the genes functionality, explaining the majority of dogs with brown coat and nose color.  One exception is the brown or chocolate French bulldog, which remained a mystery as to the cause.  In 2014 Animal Genetics sequenced the TYRP1 gene of several brown French bulldogs but was not able to find any functional variants that corresponded to brown coat color, eliminating the TYRP1 gene as the primary cause of French Bulldog chocolate.  Recently, research conducted in University of Bern in Switzerland revealed a nonsense variant in HPS3, c.2420G>A or p.(Trp807*). In this study the brown or chocolate dog was homozygous for the mutant allele.  

Animal Genetics conducted whole genome sequencing on 3 brown or chocolate French bulldogs, 2 negative for all TYRP1 allele mutations and one brown dog that carried one copy of the recessive form of a TYRP1 variant. Our research showed the same correlation between the recessive HPS3 allele and the phenotypical look of the dog. 

Differences in coat, skin and eye color between TYRP1 and HPS3 homozygous dogs are subtle but clear with two copies of cocoa having a slightly darker coat color and lighter eyes than the more common TYRP1 related brown dogs.