Cats with brown gene variants have reduced amounts of black pigment and appear brownish in color.
Phenotype: Cats with brown gene variants have reduced eumelanin (black pigment) and appear brownish in color.
Mode of Inheritance:Autosomal recessive (order of dominance is B > b > bl)
Alleles: B = Wild-type black, b= Brown (chocolate), bl = Light brown (cinnamon)
Breeds appropriate for testing: Many breeds
Explanation of Results:
Cats with B/B genotype will be full-colored and will not display chocolate or cinnamon coloration. They cannot produce chocolate or cinnamon offspring and cannot transmit these chocolate or cinnamon variants to any of their offspring.
Cats with B/b genotype will be full-colored and are carriers of chocolate. They will transmit this chocolate variant to 50% of their offspring. Matings between two carriers of chocolate are predicted to produce 25% chocolate kittens.
Cats with B/bl genotype will be full-colored and are carriers of cinnamon. They will transmit this cinnamon variant to 50% of their offspring. Matings between two carriers of cinnamon are predicted to produce 25% cinnamon kittens.
Cats with b/b genotype will be chocolate and will transmit this chocolate variant to all of their offspring.
Cats with b/bl genotype will be chocolate and are carriers of cinnamon. They will transmit this cinnamon variant to 50% of their offspring. Matings between two carriers of cinnamon are predicted to produce 25% cinnamon kittens.
Cats with bl/bl genotype will be cinnamon and will transmit this cinnamon variant to all of their offspring.
Note: Overall appearance of the cat's coat also depends on expression of and complex interactions with other genes.
The tyrosinase-related protein-1 (TYRP1) gene affects the amount of black pigment (eumelanin) produced, and mutations in this gene are known to cause brown coat color phenotypes in many species of mammal. Research by Lyons Feline Genetics Laboratory at University of California, Davis identified two mutations in this gene that cause different variations of brown coat colors in cats. The darker shade of brown coat color referred to as chocolate/chestnut results from an intronic mutation that causes a splice variant (c.1261+5G>A) which results in a truncated protein. A lighter brown variant commonly called cinnamon/red is caused by a nonsense mutation (c.298T>C) that also results in an truncated protein.
The two variants form an allelic series that lead to these shades of brown. The wild-type B allele produces normal, black coloration (full production of eumelanin). The b allele produces the brown or chocolate phenotype and the bl allele produces a light brown or cinnamon phenotype. The order of dominance in this allelic series is B dominant to b, and b dominant to bl (B > b > bl).
Lyons, L.A., Foe, I.T., Rah, H.C., & Grahn, R.A. (2005). Chocolate coated cats: TYRP1 mutations from brown color in domestic cats. Mammalian Genome, 16, 356-366. doi: 10.1007/s00335-004-2455-4
Schmidt-Küntzel, A., Eizirik, E., O'Brien, S.Y., Menotti-Raymond, M. (2005). Tyrosinase and tyrosinase related protein 1 alleles specify domestic cat coat color phenotypes of the albino and brown loci. J Hered. Jul-Aug; 96(4): 289–301. doi: 10.1093/jhered/esi066.