Coat Colour Introduction Cats

Introduction to coat colours in cats

In cats, coat colour is a complex trait shaped by the interaction of multiple genes. Mutations in these genes, often referred to as loci*, interact in intricate ways, resulting in the wide variety of coat colours and patterns seen in modern cats. Many of these loci are designated by specific letters representing the effect of the mutant allele. In breeding communities, the loci names are often more familiar and commonly used than the actual gene names.

The original coat colour of the domestic cat, like that of its wild ancestors, is tabby: a mixture of dark and light bands of fur, resulting in distinctive thin stripes along the head, legs, body and tail. These colours are produced by two types of pigment: eumelanin (dark pigment; appears dark brown or black) and phaeomelanin (light pigment; appears as brownish/red to yellow), with white hair indicating a lack of either pigment.

The mutations affecting coat colour either impact the production of these pigments or their distribution on the body. For instance, the recessive non-agouti mutation at the A-locus leads to an even distribution of dark pigment across the body instead of limiting it to tabby stripes, resulting in an evenly black colour. Conversely, both the X-linked Orange mutation and recessive mutations at the E-locus limit the production of dark pigment, resulting in an entirely red-orange coat with fainter stripes.

These coat colour mutations can interact with each other, for example as seen when a cat carries both the D-locus dilution and B-locus brown mutations, resulting in a diluted brown coat known as lilac or lavender. However, certain mutations can counteract or exclude each other’s effects. For instance, an orange cat will not display the effects of the B-locus brown mutation, since it lacks black hairs to turn brown in the first place.

X-Linked Orange, also known as the O-locus, is an unusual factor in coat colour. The mutation is co-dominant, and carriers randomly develop patches of fur expressing either the mutant orange coat or their normal colouration (typically black or tabby). This is what results in tortoiseshell and calico coats (the latter being when the cat also expresses a gene for white spotting). As the gene is X-linked, males cannot normally be carriers, and will therefore never display tortoiseshell patches. (There are exceptions, such as an XXY karyotype or chimerism, but these are extremely rare.) The exact mutation is currently unknown, and no test can be performed on the O-locus.

*Loci (singular: locus) refer to specific locations on a chromosome where a gene or mutation is found.

Tested coat colour and pattern loci

• D-Locus – Dark coat becomes dilute/grey, often called Blue
• C-Locus – The colour-point mutations distinctive of the Siamese and Burmese breeds, as well as more complete forms of albinism
• E-Locus – Coat becomes red, often called Amber, Russet or Copal
• W-Locus – Coat gains white sections, up to an entirely white body. May also cause hearing loss.
• B-Locus – Dark coat becomes brown, often called Cinnamon or Chocolate
• Gold – Coat becomes warm shades of yellow and orange, sometimes called Sunshine
• A-Locus & Tabby mutations – A group of mutations affecting the distribution of dark and light fur. Includes non-agouti (black coat), Charcoal (modification of Bengal coat), Ticked (sandy coat) and Blotched (broader, thicker tabby stripes)
• G-Locus – Feet gain white “gloves”