E-Locus Cat (Amber, Russet)

E-Locus (Amber, Russet)

In cats, several different genes can be responsible for an orange or red coat colour. The most well-known variant, the X-linked Orange mutation (responsible for orange, tortoiseshell and calico coats) is discovered in 2024 and will soon be available. There are also other mutations that can result a similar reddish colouration.

The Extension Locus (E-Locus) corresponds to the gene ‘melanocortin 1 receptor’ (MC1R), which is involved in the regulation of pigment production. Active MC1R causes a cell to “switch” from the production of phaeomelanin (yellow/red pigment) to eumelanin (black/brown pigment). Mutations affecting the E-locus often result in a lightening of the coat, from black/brown to red/yellow/white.

Inheritance

The wild-type form of the E-Locus is designated as ‘E’ (no mutation). Cats with at least one E-allele are able to produce dark coat pigment. However, this darker coat may be further affected by other coat colour loci such as the B-Locus and D-Locus. The recessive mutations designated as ‘e’ interrupt the function of MC1R. Cats with two e-alleles have lighter coats, in various shades of yellow, red or orange. Depending on the breed, this colour may be designated as amber, russet, red or copal.

Relevant tests

• K306
• K639