Cat coat genetics

Cat coat genetics determine the coloration, 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 could wear point coloration, the stereotypical coat of a Siamese.

Solid colors

Eumelanin and phaeomelanin

Eumelanin

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

Sex-linked red

The sex-linked red "Orange" locus, O/o, determines whether a cat will produce eumelanin. In cats with orange fur, phaeomelanin completely replaces eumelanin. 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, 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 calicos 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 pelt color 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 color, but it can also present as a yellow or light ginger color. Unidentified "rufousing polygenes" are theorized to be the reason for this variance.
Orange is epistatic to nonagouti, 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 color associated with the Orange locus is the result of a genomic deletion in a regulatory region of , a Rho GTPase activating protein. The deletion results in a 13-fold increase in expression of the protein in melanocytes.

Dilution

The Dense pigment gene, D/d, codes for melanophilin, a protein involved in the transportation and deposition of pigment into a growing hair. When a cat has two of the recessive d alleles, black fur becomes "blue", chocolate fur becomes "lilac", 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.

Basic color	Dilution	Dilute modifier, double dilution
Black	Blue	Caramel, blue-based caramel
Chocolate	Lilac	Taupe, lilac-based caramel
Cinnamon	Fawn	Fawn-based caramel
Red	Cream	Apricot
Amber	Light amber	Unknown
White	N/A	N/A

Other genes

Barrington Brown is a recessive browning gene that dilutes black to mahogany, brown to light brown and chocolate to pale coffee. It is different from the browning gene and has only been observed in laboratory cats.
The Dilution modifier gene, Dm, "caramelizes" the dilute colors as a dominant trait. The existence of this phenomenon as a discrete gene is a controversial subject among feline enthusiasts.
Amber, a mutation at the extension locus E/e changes black pigment to amber or light amber, similar in appearance to red and cream. Kittens are born dark but lighten up as they age. Paws and nose still exhibit the original undiluted color in contrast to other diluted colors, where paws and nose have the diluted color. This phenomenon was first identified in Norwegian Forest cats.
Another recessive mutation at extension was discovered which causes the russet color in Burmese cats. It is symbolized as e^r. Like amber cats, russet cats lighten as they age.
A modifying factor has also been hypothesized in shaded silver and chinchilla Persians whose fur turns pale golden in adulthood, due to low levels of phaeomelanin production. These cats resemble shaded or tipped goldens, but are genetically shaded or tipped silvers. This is probably related to the phenomenon known as "tarnishing" in silvers.
Tabbies

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. However, the following different coat patterns are all possible:

Mackerel: Thin, dark stripes
Blotched/Classic: Thicker bands or whorls of dark pigment.
Spotted: Broken bands that look more like individual spots.
Ticked: No distinct stripes, spots, or blotches on the body—though some may be visible on the legs, face, and tail.
Agouti

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 signaling protein. 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 in bright slanted light on kittens and on the legs, tail and sometimes elsewhere on adults.
A major exception to the solid masking of the tabby pattern exists, as the O allele of the O/o locus is epistatic over the aa genotype. That is, in red or cream colored cats, tabby marking is displayed regardless of the genotype at the agouti locus. However, some red and most cream tabbies do have a fainter pattern when lacking an agouti allele, indicating that the aa genotype does still have a faint effect even if it does not induce complete masking. The mechanism of this process is unknown.
An example of the Agouti gene can be seen in Bengal cats, which are a hybrid between Asian Leopard cats and domestic cats. The breed has a characteristically dark face marking and a stripe down its back. This is term as a and , as well as charcoal markings, according to Gershoney et. al. The charcoal mask is indicated to be the result of a heterozygote of The relationships between the different agouti alleles is not fully understood. More research to required to determine "modes of inheritance for charcoal" in Bengal cats.

Dark markings

The Tabby locus on chromosome A1 accounts for most tabby patterns seen in domestic cats, including those patterns seen in most breeds. The dominant allele Ta^M produces mackerel tabbies, and the recessive Ta^b produce classic tabbies. The gene responsible for this differential patterning has been identified as transmembrane aminopeptidase Q. A threonine to asparagine substitution at residue 139 in this protein is responsible for producing the tabby phenotype in domestic cats. In cheetahs, a base pair insertion into exon 20 of the protein replaces the 16 C-terminal residues with 109 new ones, generating the king cheetah coat variant.
The wild-type is the mackerel tabby. The most common variant is the classic tabby pattern. Spotted tabbies have their stripes broken up into spots, which may be arranged vertically or horizontally. A 2010 study suggests that spotted coats are caused by the modification of mackerel stripes, and may cause varying phenotypes such as "broken mackerel" tabbies via multiple loci. If the genotype is Sp/Sp or Sp/sp the tabby coat will be spotted or broken. If it is an sp/sp genotype, the tabby pattern will remain either mackerel or blotched. This gene has no effect on cats with a ticked coat.

Ticked tabby

The Ticked locus on chromosome B1 controls the generation of "ticked coats", agouti coats with virtually no stripes or bars. Ticked tabbies are rare in the random-bred population, but fixed in certain breeds such as the Abyssinian and Singapura. Ti^A is the dominant allele that produces ticked coats; Ti⁺ is the recessive one. The causative gene for ticked tabby markings is Dickkopf-related protein 4. Both a cysteine to tyrosine substitution at residue 63 and an alanine to valine substitution at residue 18 result in decreased DKK4, which is associated with ticking. Both variants are present in the Abyssinian breed, and the A18V variant is found in the Burmese breed. Stripes often remain to some extent on the face, tail, legs, and sometimes the chest. Traditionally, this has been thought to happen in heterozygotes but be nearly or completely nonexistent in homozygotes. The ticked tabby allele is epistatic to and therefore completely masks all the other tabby alleles, "hiding" the patterns they would otherwise express.
It was once thought that Ti^A was an allele of the Tabby gene, called T^a, dominant to all other alleles at the locus.