Genetic basis of The Chocolate and Cinnamon coat colours - in cats are caused by mutations in the TYRP1 gene (tyrosinase-related protein 1), located at the B locus. This gene encodes an enzyme important in the production of eumelanin (the black pigment). The B locus has three main alleles with a dominance hierarchy: B (wild-type black) > b (chocolate) > b1 (cinnamon). Cats with BB, Bb, or Bb1 genotypes show a black (or brown depending on dilution) phenotype. Cats with bb or bb1 genotypes have the chocolate phenotype, a rich dark brown colour. Cats with b1b1 genotype show the cinnamon phenotype, a lighter, reddish-brown shade. These are autosomal recessive traits, meaning a cat must inherit two copies of the respective allele for chocolate or cinnamon colour to be visible.
Pathophysiology - TYRP1 influences eumelanin production by converting dopachrome during melanin synthesis. The mutations causing chocolate and cinnamon alter the TYRP1 enzyme such that: The brown variants produce altered eumelanin pigment granules: chocolate granules are somewhat elongated, cinnamon granules even longer and lighter, which changes light absorption and coat colour. Chocolate and cinnamon cats have reduced or modified black pigment, resulting in the characteristic brownish coat shades. The mutation does not affect phaeomelanin (yellow/red pigment), so red-based colours are unchanged.
Complications - There are no known health issues associated with chocolate or cinnamon coat colours; these mutations only affect coat pigmentation. However: Chocolate and cinnamon alleles are rare and breed-specific, so breeders should be aware of testing and genetics to maintain diversity. Coat colour appearance can be influenced by other pigment or dilution genes, so phenotypic prediction requires comprehensive genetic information.
Why This Matters to Breeders and Vets - Breeders use genetic testing to identify carriers and plan matings to produce or avoid chocolate and cinnamon coats. This helps meet breed standards and aesthetic goals. Veterinarians benefit from understanding these genotypes to advise breeders or owners on inheritance and possible phenotypic outcomes. DNA tests are available from specialized labs to detect these alleles reliably. Awareness helps maintain genetic diversity and avoid inadvertent breeding of rare colour variants without genetic knowledge.
Summary - Chocolate and Cinnamon coat colours in cats result from mutations in the TYRP1 gene at the B locus, which affect eumelanin pigment production. Chocolate (dark brown) is caused by the b allele (homozygous bb or compound heterozygous bb1), while cinnamon (light reddish-brown) is caused by the b1 allele (homozygous b1b1). Both are autosomal recessive traits. These colours are purely cosmetic with no health impact. DNA testing facilitates precise breeding decisions and genetic management of these rare and desirable coat colours.