Cat coat genetics

Eumelanin and phaeomelanin

Sex-linked red

Basic colours

A male red tabby showing the X^OY-phenotype

A female black tortoiseshell cat showing the X^OX^o-phenotype

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).^[2] 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.^[3] 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.^[4] 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.^[4]

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.^[5]

The identity of the gene at the Orange locus was narrowed down to a 3.5 Mb stretch on the X chromosome in 2009.^[5] 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.^[6][7]

Dilution

Diluted colours

A cream (diluted red) tabby cat

A blue (diluted black) tortoiseshell cat

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.^[5] 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".^[8] 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.^[5]

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.^[9]
• The Dilution modifier gene, Dm, "caramelises" the dilute colours as a dominant trait. The existence of this phenomenon as a discrete gene is a controversial subject among feline enthusiasts.^{[citation needed]}
• Amber, a mutation at the extension locus E/e (the melanocortin 1 receptor; MC1R) 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 colour in contrast to other diluted colours, where paws and nose have the diluted colour. This phenomenon was first identified in Norwegian Forest Cats.^[10]
• Another recessive mutation at extension was discovered which causes the "russet" colour in Burmese cats. It is symbolised as e^r. Like amber cats, russet cats lighten as they age.^[11]
• A modifying factor has also been hypothesised 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.

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 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.^[12] 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.

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 coloured 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 sports the hybrid 'charcoal' pattern, a pseudomelanistic marking which has a characteristic dark face marking, the "mask", and a broad dorsal stripe down its back, the "cape".^[13][14] According to Gershoney et. al., the charcoal mask is indicated to be the result of a heterozygote of A^Pbe/a.^[13] The relationships between the different agouti alleles is not fully understood. More research is required to determine the inheritance modes for charcoal.^[14]

Tabby 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 (sometimes referred to as blotched) tabbies.^[15] The gene responsible for this differential patterning has been identified as transmembrane aminopeptidase Q (Taqpep, M3XFH7).^{[citation needed]} A threonine to asparagine substitution at residue 139 (T139N) 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 (N977Kfs110), generating the king cheetah coat variant.^[16]

The wild-type (in African wildcats) is the mackerel tabby (stripes look like thin fishbones and may break up into bars or spots). The most common variant is the classic tabby pattern (broad bands, whorls, and spirals of dark colour on pale background usually with bulls-eye or oyster pattern on flank).^[16] 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.^[15]

Other genes

• Other genes (pattern modifier genes) are theorised to be responsible for creating various type of spotting patterns, many of which are variations on a basic mackerel or classic pattern. There are also hypothetical factors which affect the timing and frequency of the agouti shift, affecting agouti band width and the number and quality of alternating bands of eumelanin and phaeomelanin on individual hairs.
• There is a gene not yet identified, but believed to be related to the agouti gene in the Chausie breed that produces silver-tipped black fur similar to Abyssinian ticked fur, known as "grizzled". This phenomenon is purported to have been inherited from the hybridisation of the domestic cat to the jungle cat (Felis chaus).
• The rosette tabby pattern is a pattern similar to that of a leopard, where rosette spots are spread over the body. The pattern is found in hybrid cat breeds, such as the Bengal and Safari.^{[20][unreliable source]}
• The inhibited pigment gene, I/i. The dominant allele (I) produces tipped hairs that are fully coloured only at the tip and have a white base. This allele appears to interact with other genes to produce various degrees of tipping, ranging from deeply tipped silver tabby to lightly tipped shaded silver and chinchilla silver. The inhibitor gene interacts with the non-agouti genotype (I-aa) to produce the colour known as smoke. The homozygous recessive genotype when combined with the agouti gene (iiA-), produces tabby colouration, which can vary along a spectrum ranging from a deeply patterned brown tabby, to a lighter "golden tabby", to the very lightly coloured shaded or chinchilla golden colours. Red and cream cats with the inhibitor gene (I-O-) are commonly called "cameo".

Tricolour cats

Tortoiseshells with white spotting are known as "tricolour" or "tortoiseshell and white".^[a][23] Those with approximately 25–75% white are known in the North America as "calico".^[23][24] A tricolour consist of three colours: white, a phaeomelanin red-based colour (red or cream), and eumelanin black-based colour (e.g. black or blue).

In tricolour cats, the factor that distinguishes brindled patterns from distinct patches is the placement of eumelanin and phaeomelanin pigment, which is partly dependent on the amount of white, due to an effect of the white spotting gene on the general distribution of melanin. A cat which has both an orange and non-orange gene, Oo, and little to no white spotting, will present with a brindled (mottled) blend of black-based and red-based pigments, reminiscent of tortoiseshell material (called tortoiseshell cat in the US). An Oo cat with a large amount of white will have bigger, clearly defined patches of black-based and red-based pigments (called a "calico" in the US).

Variations

• The basic tortoiseshell pattern has several different colours depending on the colour of the eumelanin (the B locus), and dilution (the D locus).
• Tortoiseshell tabbies, also known as torbies, display tabby patterning on both red- and black-based colours. Calico tabbies are colloquially also called calibys or tabicos.^[b][2] Tortoiseshell cats with small white patches are called tortico cats, a portmanteau of calico and tortoiseshell.^{[b][25][failed verification]} Blue tortoiseshell (US: diluted calico) cats have a lighter colouration (blue/cream) and are sometimes called calimanco or clouded tiger.^[b][26]

Silver series

The silver series is caused by the melanin inhibitor gene I/i. The dominant form causes melanin production to be suppressed, but it affects phaeomelanin (warm red pigment) much more than eumelanin (black or brown pigment). On tabbies, this turns the background colour into a sparkling cold silver tone. The dark hairs that make the tabby pattern will be silvery-white at their roots, whilst leaving the pigmentation at the tip of these hairs intact, resulting in a cold-toned silver tabby. On solid cats, it turns the base of the hair throughout their coat into a depigmented pale silvery-white, whilst the tip stays pigmented, making them (silver) smoke.^[39] The term cameo is commonly used for red silver and cream silver (inhibitor gene (I-O-)) coloured coats in cats.

Wide-band factors

Silver agouti cats can have a range of silver tabby phenotypes depending on the depigmentation ratio of the hair root to tip; from regular silver tabby (over half the hair is pigmented), to the more extreme silver tabby forms of silver shaded (under half the hair is pigmented, approx. ⅓ of hair length), and silver tipped also called 'chinchilla' or 'shell' (only the very tip of the hair is pigmented, approx. ⅛ of hair length). This seems to be affected by hypothetical wide-band factors, which make the silver band at the base of the hair wider in silver tabbies and smokes. Breeders often notate wide-band as a single gene Wb/wb, but it is most likely a polygenic trait.

• 
  Smoke / silver tabby
• 
  Shaded – ⅓
• 
  Tipped – ⅛ ("chinchilla" / "shell")
• 
  red or cream silver ("cameo")

Golden series

If a cat has the wide-band trait but no silver melanin inhibitor, the band will be golden instead of silver. These cats are known as golden tabbies, or in Siberian cats as sunshine tabbies. The golden colour is caused by the CORIN gene. Shaded golden and tipped golden are also possible, in the same hair length distribution as the silver-gene. However, there is no golden smoke, because the combination of wide-band and non-agouti simply produces a solid cat.^{[40][41][unreliable source]}

Wide-band expression

The genetics involved in producing the ideal tabby, tipped, shaded, or smoke cat is complex. Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another. For example, the silver melanin inhibitor gene in some instances does not block pigment, resulting in a greyer undercoat, or in tarnishing (yellowish or rusty fur). The greyer undercoat is considered less desirable to fanciers.

Likewise, poorly-expressed non-agouti or over-expression of melanin inhibitor will cause a pale, washed out black smoke. Various polygenes (sets of related genes), epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of colouration, some deemed more desirable than others by fanciers.

The genetic influences on tipped or shaded cats are:

• Agouti gene.
• Tabby pattern genes (such as T^a masking the tabby pattern).
• Silver/melanin inhibitor gene I/i.
• Golden CORIN gene.
• Factors affecting the number and width of bands of colour on each hair, such as the hypothetical wide-band gene wb. Resulting in shaded or tipped (chinchilla/shell) pigmentation.
• Factors affecting the amount and quality of eumelanin and/or phaeomelanin pigment expression (such as the theorised rufousing factors)
• Genes causing sparkling appearance (such as glitter in the Bengal, satin in the Tennessee Rex, grizzle in the Chausie).
• Factors to clear up residual striping (hypothetical Chaos, Confusion, Unconfused, Erase, and Roan factors).

• Silver series
• 
  Black silver spotted tabby Egyptian Mau.
• 
  Black smoke Egyptian Mau with 'ghost markings'
• 
  Red silver ("cameo") shaded Maine Coon.
• 
  Black silver tipped ("chinchilla") Persian.
• 
  Black tortoiseshell silver shaded Domestic Longhair.

• Golden series
• 
  Sunshine blotched tabby Siberian Cat.
• 
  Black golden ticked tabby British Shorthair.
• 
  Black golden ticked tabby British Shorthair.
• 
  Blue golden tipped ("chinchilla") Persian.

Cat coat hair

Cat fur can be short, long, curly, or hairless. Most cats are short-haired, like their wild ancestor.^[46] The fur can naturally come in three types of hairs; guard, awn, and down hair. The length, density and proportions of these three hairs varies greatly between breeds, and in some cats only one or two types are found.^[46][47]

Most oriental breeds only express one single layer of silky coat.^[46] However, cats can also have double-layered coats out of two hair types in which the down hairs form the soft, insulating undercoat, and the guard hairs form the protective outer coat.^[46]

A typical cat coat exists of all three natural hair types, but due to the equal lengths of two of these hairs, the coat is still considered double-layered.^[46] Typically, the down hairs comprise the undercoat while the guard and awn hairs make up the basic top coat.^[46][47] Double-coated cats with thick undercoats require daily grooming as these coats are more prone to matting.^[46] Double coats are found in for example the Persian, British Shorthair, Maine Coon and Norwegian Forest Cat.

Additionally, there even exist cats which express all three natural types of cat hair in different lengths and structures, which form three different layers. These cats are called triple-coated. Siberians and Neva Masquerades are known for their unique triple coats,^[46] which provided their landrace ancestors with extra insulation to withstand their arctic habitat.

Coat mutations

There have been many genes identified that result in unusual cat fur. These genes have been discovered in random-bred and purebred cats worldwide, and are sometimes selectively bred into new breeds or breed varieties. Some of the genes are in danger of going extinct because the cats are not sold beyond the region where the mutation originated or there is simply not enough demand for cats expressing the mutation.

In many breeds, coat gene mutations are perceived as unfavourable. An example is the rex allele which appeared in Maine Coons in the early 1990s in Germany, the UK and the US.

Fur length

Cat fur length is governed by the Length gene in which the dominant form, L, codes for short hair, and the recessive l codes for long hair. In the longhaired cat, the transition from anagen (hair growth) to catagen (cessation of hair growth) is delayed due to this mutation.^[48] A rare recessive shorthair gene has been observed in some lines of (silver) Persian where two longhaired parents have produced shorthaired offspring.

The Length gene has been identified as the fibroblast growth factor 5 (FGF5; M3X9S6) gene. The dominant allele codes for the short coat is seen in most cats. Long coats are coded for by at least four different recessively inherited mutations, the alleles of which have been identified.^[49] The most ubiquitous is found in most or all long haired breeds while the remaining three are found only in Ragdolls, Norwegian Forest Cats, and Maine Coons.

Curly-coated

Main article: Rex mutation

There are various genes producing curly-coated or "rex" cats. New types of rex arise spontaneously in random-bred cats now and then. Some of the rex genes that breeders have selected for are:

• Devon Rex
  • Mutation in KRT71 (E1AB55), the same gene causing hairlessness in Sphynx cats. re is an allele completely recessive to the wildtype and completely dominant to hr found in Sphynx.^[50]
• Cornish Rex
  • Mutation in LPAR6 (A0A5F5XLZ8). A completely recessive allele termed r.^[51]
• Ural Rex
  • Mutation in LIPH.^[52]
• German Rex
  • Provisionally an allele termed gr. Same locus as Cornish, but proposed as a different allele. However, most breeders consider the German Rex to have r/r genotype.
• Oregon Rex (extinct)
  • A hypothetical recessive allele termed ro.
• Selkirk Rex
  • A dominant allele termed Se, although sometimes described as an incomplete dominant because the three possible allele pairings relate to three different phenotypes: heterozygous cats (Se/se) may have a fuller coat that is preferred in the show ring, while homozygous cats (Se/Se) may have a tighter curl and less coat volume. (se/se type cats have a normal coat.) This phenomenon may also colloquially be referred to as additive dominance.
• LaPerm
  • Provisional completely dominant Lp allele.