Russet Coat (MC1R gene, Burmese)

The "russet" trait in Burmese cats is a reddish coloration that develops with age and is caused by a variant in the MC1R gene, also known as the extension locus (E locus).

Definition

The russet color is a reddish coat color identified in Burmese cats. This color can vary from birth to adulthood, starting with a tabby-like coloration that gradually becomes lighter or reddish, especially on the head. This coloration is caused by a mutation in the MC1R (melanocortin 1 receptor) protein, which regulates the amount of eumelanin (dark pigment) and pheomelanin (light pigment). Activation of MC1R leads to the formation of dark coat, while inactivation of MC1R results in a lighter coat.

Genetic basis

The e^r allele is responsible for the russet coat in the Burmese breed and is due to a c.440_442del deletion in the MC1R gene. This variant follows an autosomal recessive mode of inheritance, which means that two copies of the variant are required to express this coat coloration. The presence of a single copy does not produce the russet phenotype, but it can be transmitted to offspring with a 50% probability.

Other relevant information

The c.440_442del deletion affects the amount and distribution of melanin according to body temperature. The limbs and face of Burmese cats are darker due to the lower temperature in these areas, which increases the activity of tyrosinase, a key enzyme in melanin production.

Bibliography

Gustafson NA, Gandolfi B, Lyons LA. Not another type of potato: MC1R and the russet coloration of Burmese cats. Anim Genet. 2017;48(1):116-120.