Locus B (Brown - chocolate, cinnamon)

The locus B is responsible for the brown coat colour, namely the variants in TYRP1 gene (tyrosinase-related protein 1), which is associated with this locus. In cats, a series of alleles B˃b˃bl has been described.

The allele B is the original (wild type) allele and determines the dark colour; the B-allele is dominant in this series.

In connection with b-allele (chocolate), the variants c.8C˃G (p.A3G) and c.1262+5G˃A have been described.

The variant c.298C˃T (p.R100X) has been described in connection with b^l -allele (cinnamon) (Lyons et al. 2005).

The brown and cinnamon colour is autosomal recessively inherited colour, i.e. the phenotype comes to expression only in cats which inherited these b-alleles from their parents. A cat with genotype b/b has a chocolate-brown colour and a cat of genotype b^l/b^l has a light brown (cinnamon) colour.

Example of cinnamon coat color:

.

Example of chocolate coat color:

.

Genotypes:

• a cat with B/B genotype transmits neither b-allele (for chocolate colour) nor b^l -allele (for cinnamon colour)
• a cat with B/b genotype is a carrier of b-allele b (chocolate)
• a cat with B/b^l -genotype is a carrier of b^l -allele (cinnamon )
• a cat with b/b-genotype with chocolate-brown colour (homozygous for chocolate allele - this individual always passes this allele on to its offsprings)
• a cat with b/b^l -genotype with chocolate-brown colour is a carrier of bl-allele (cinnamon)
• a cat with b^l /b^l -genotype with cinnamon colour (homozygous for cinnamon allele - this individual always passes this allele on to its offsprings)