Coat Colour C-Locus Colourpoint (Siam, Mink, Burma)

Coat colour in cats is controlled by a wide range of different genes working together. One of these genes involved is the Tyrosinase (TYR) gene. This gene produces an enzyme that is required for melanin production, which gives skin, hair, and eyes their colour. Mutations in this gene cause various degrees of Type 1 Oculocutaneous Albinism (OCA1), a failure to produce pigment. This can range between the distinctive point colouration of the Burmese and Siamese cat, to complete albinism.

Two known autosomal recessive mutations in TYR have been associated with colourpoints: a pattern of coloration that causes a cat’s body to be pale and their extremities to be dark. It is directly caused by temperature differences in which the darker parts of the cat are colder, while the lighter parts are warmer. The first mutation is designated as “cb” and is responsible for Burmese-type point colouration or Burmese colourpoint. The second mutation is designated as “cs” and is responsible for Siamese-type point colouration or Siamese colourpoint. Cats that carry one “cb” allele and one “cs” allele will display Tonkinese or Mink colourpoints instead, an intermediate color between Siamese and Burmese. The “cb” and “cs” variants are both tested here.

The alleles of the mentioned mutations are equal in dominance. They are recessive to the normal genotype (C) and dominant over the alleles for complete albinism (c and c2).