Red-brown colouration in Burmese cat

The E (Extension) locus encodes the melanocyte stimulating hormone receptor (MC1R). While the dominant E allele causes the synthesis of eumelanin, which is responsible for the dark coloration (black or brown), the recessive e allele caused by the mutation results in the loss of function of the MC1R gene and produces pheomelanin, which is responsible for the light coloration (red or yellow).

Mutation c.440_442del causes reddish-brown colour by suppressing the function of the MC1R gene. Kittens are born dark with a reddish tinge, during the first year eumelanin gradually disappears from the coat and the colour lightens. Adults show an apricot-red colour.

Inheritance of the mutation is autosomal recessive. This means that the reddish-brown colour will appear in individuals who have inherited the mutated e^r allele from both parents (recessive homozygotes). Heterozygotes are carriers of the mutated gene.

References:

Gustafson, N.A., Gandolfi, B., Lyons, L.A. : Not another type of potato: MC1R and the russet coloration of Burmese cats. Anim Genet 48:116-120, 2017. Pubmed reference: 27671997.