Cat coat genetics

Cat coat genetics determine the colouration, pattern, length, and texture of feline fur. The variations among cat coats are physical properties and should not be confused with cat breeds. A cat may display the coat of a certain breed without actually being that breed. For example, a Neva Masquerade (Siberian colourpoint) could wear point colouration, the coat typically associated with a Siamese.

The browning gene B/b/b^l codes for TYRP1 (Q4VNX8), an enzyme involved in the metabolic pathway for eumelanin pigment production. The dominant form, B, will produce black eumelanin. It has two recessive variants, b (chocolate) and b^l (cinnamon), with b^l being recessive to both B and b. Chocolate is a rich dark brown colour, and is referred to as chestnut in some breeds. Cinnamon is a light brown which may be a reddish colour.

The sex-linked red "Orange" locus, O/o, determines whether a cat will produce eumelanin. In cats with orange fur, phaeomelanin (red pigment) completely replaces eumelanin (black or brown pigment). This gene is located on the X chromosome. The orange allele is O, and non-orange is o. Males are typically only orange or non-orange due to only having one X chromosome. Since females have two X chromosomes, they have two alleles of this gene. OO results in orange fur, oo results in fur without any orange (black, brown, etc.), and Oo results in a tortoiseshell cat, in which some parts of the fur are orange and other areas non-orange. One in three thousand tortoiseshell cats are male, making the combination possible but rare - however, due to the nature of their genetics, male tortoiseshells often exhibit chromosomal abnormalities. In one study, less than a third of male tortoiseshells had a simple XXY Klinefelter's karyotype, slightly more than a third were complicated XXY mosaics, and about a third had no XXY component at all.

The coat colour commonly referred to as "orange" is scientifically known as red. Other common names include yellow, ginger, and marmalade. Red show cats have a deep orange colour, but it can also present as a yellow or light ginger colour. Unidentified "rufousing polygenes" are theorised to be the reason for this variance. Orange is epistatic to non-agouti, so all red cats are tabbies. "Solid" red show cats are usually low contrast ticked tabbies.

The identity of the gene at the Orange locus was narrowed down to a 3.5 Mb stretch on the X chromosome in 2009. In 2024 it was discovered that the dominant orange colour associated with the Orange locus is the result of a genomic deletion in a regulatory region of ARHGAP36, a Rho GTPase activating protein. The deletion results in a 13-fold increase in expression of the protein in melanocytes.

The Dense pigment gene, D/d, codes for melanophilin (MLPH; A0SJ36), a protein involved in the transportation and deposition of pigment into a growing hair. When a cat has two of the recessive d alleles (Maltese dilution), black fur becomes "blue" (appearing grey), chocolate fur becomes "lilac" (appearing light, almost greyish brown-lavender), cinnamon fur becomes "fawn", and red fur becomes "cream". Similar to red cats, all cream cats are tabbies. The d allele is a single-base deletion that truncates the protein. If the cat has d/d genes, the coat is diluted. If the genes are D/D or D/d, the coat will be unaffected.

Tabby cats have a range of variegated and blotched coats, consisting of a dark pattern on a lighter background. This variety is derived from the interplay of multiple genes and resulting phenotypes. Most tabbies feature thin dark markings on the face, including the 'M' on the forehead and an eyeliner effect, pigmented lips and paws, and a pink nose outlined in darker pigment.^{[citation needed]} The following tabby coat patterns are all naturally found in the domestic cat:^{[citation needed]}

The agouti factor determines the "background" of the tabby coat, which consists of hairs that are banded with dark eumelanin and lighter phaeomelanin along the length of the hair shaft. The Agouti gene, with its dominant A allele and recessive a allele, controls the coding for agouti signalling protein (ASIP; Q865F0). The wild-type dominant A causes the banding and thus an overall lightening effect on the hair, while the recessive non-agouti or "hypermelanistic" allele a does not initiate this shift in the pigmentation pathway. As a result, homozygous aa have pigment production throughout the entire growth cycle of the hair and therefore along its full length. These homozygotes are solidly dark throughout, which obscures the appearance of the characteristic dark tabby markings—sometimes a suggestion of the underlying pattern, called "ghost striping", can be seen, especially on kittens and on adults in bright slanted light, in smokes, and sometimes on the forehead, legs, tail or elsewhere.