Brown or chocolate coat color is frequent in many dog breeds due to variants at the B locus on TYRP1 gene. In French bulldog two variants in two different genes (TYRP1 and HPS3) were associated with brown coat color. There are subtle but clear differences in coat, skin and eye color between TYRP1 and HPS3 homozygous dogs. Dogs with two copies of HPS3 mutation have a slightly darker coat color and lighter eyes than the TYRP1 related brown dogs. The HPS3 gene related brown coat color in French bulldog was named cocoa. Cocoa in adult dogs appears slightly darker as in young dogs.
Different research shows that most of brown French bulldogs are due to variants on HPS3 gene or/and TYRP1 gene. Findings of one research group and testing data in our laboratory suggest that a small number of brown French bulldogs do not possess any of the causal variants. We therefore anticipate that there are some other, yet uncharacterized causal variants, which can cause brown colour in French bulldogs.
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N/N
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Variant for cocoa is not present. The dog will always pass on the 'N' allele to any potential offspring.
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CO/N
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The dog carries one copy of 'cocoa' alelle and one copy of 'N' alelle. There is a 50% probability to transfer the 'cocoa' allele to the offspring.
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CO/CO
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The dog carries two copy of 'cocoa' alelle and it will express cocoa coat colour. The dog will transfer one recessive 'cocoa' allele to its entire offspring.
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