cat coat genetics

Cat coat genetics are surprisingly intricate! This page is a guide to what I know.

Colours and Patterns

  • One gene position is for “black”. The dominant gene found at this position is B, which indeed means “black”. (Not pure black necessarily – patterns come into it later.) There are two recessive variants, b for “chocolate” fur and bl for “cinnamon”.
  • On the X chromosome is a gene position for “orange”. The genes found here are either O (for yes to orange) or o (for no orange). Because most boy cats only have one X chromosome, most of them only have one copy of this gene; girl cats have two. A boy cat will be ginger if he has the O gene, and not ginger if he has the o gene. A girl cat can have OO (ginger), Oo (tortoiseshell) or oo (no orange colouring) genes. Boy tortoiseshells are very rare and where they exist they’re usually sterile. This is because to have the two X chromosome required, they have to be either mosaic/chimeras, or intersex, with Klinefelter’s syndrome.
  • A third gene can result in lightened cat fur. If a cat has double copies of a recessive gene dd, black fur becomes grey (called “blue” by cat breeders), chocolate becomes light grey-brown (called “lilac” by cat breeders), cinnamon fur becomes fawn, and orange fur becomes cream. If the cat has even a single copy of the dominant D gene, they have the “dark” variant of the fur.
  • Tabby cats have what is called an “Agouti gene”. The Agouti gene just determines whether a cat is a tabby (in non-orange cats); their actual pattern is controlled by a different gene. Most of the time a cat lacking the Agouti gene will be solid-coloured or solid-and-white (e.g. black, grey-and-white, etc.). Note that the orange gene supersedes the Agouti gene, so an orange cat can have a tabby pattern even if it doesn’t have the Agouti gene. (In a tortoiseshell, they’ll only have the tabby pattern in their orange patches in that case.)
  • The Tabby gene controls the pattern of a tabby, as mentioned. There are two main variants a cat can have: TaM produces the “mackerel” tabby pattern, while Tab produces the “classic” pattern with whorls, spirals and broad bands of colour.
  • There is a dominant gene Sp which “breaks up” a mackerel or classic pattern into spots. The recessive gene is for no alteration, just plain mackerel or classic pattern. It has no effect on ticked tabbies, though.
  • The Ticked tabby gene is rare in “random-bred” cats but is bred for in some breeds, including Abyssinians. This is where the individual strands of fur have multiple colours (like tabbies), but the outer layer lacks a pattern like mackerel or classic. This results in cats with a kind of “ripply”-looking fur coat, or maybe one reminiscent of a static screen on a non-functioning TV.
  • The KIT gene controls how much white a cat’s coat exhibits! If a cat has a WD gene, they are dominant white (and this is the gene linked to deafness, because even the hairs on the inside of a cat’s ears can be coloured white and then they don’t work as well). WS is for “white spotting”; if a cat has one copy of this gene they are 0–50% white and if they have two copies they are 50–100%. w is the “wild-type” gene for no white. There is also a W9 gene found at this location which is specific to Birmans.
  • In American English, the difference between a calico and a tortoiseshell is in the amount of white they display. A cat which is over 50% white will have big solid blotches of black and orange, which Americans call a calico. The less white that a cat has, the more likely it is a cat will demonstrate a mottled black-orange coat pattern rather than a splotchy one; Americans call that tortoiseshell. In Australian English they are both called tortoiseshells 😂 A splotchy colouring with tabby pattern results in a kind of cat sometimes called a “torbie”.
  • There is a pattern known as colourpoint, which can be the result of one of two recessive genes at a common location. cs is Siamese-pattern colourpointedness, and cb is Burmese-pattern colourpointedness (which is the same but lower contrast). The colourpoint pattern itself means that cooler parts of a cat’s body (face/snout, ears, legs, tail) have darker fur, and warmer parts have paler fur. They’re different shades of the same underlying colour though.
  • There’s a melanin inhibitor gene, which makes cats’ fur lighter, but affects orange fur waaay more than black fur (leaving tabbies’ dark stripes basically intact, for example). If a tabby has this gene, it’ll make them a silver tabby (no evident orange or tan colouring). If a solid-patterned cat has the gene, you get a “silver smoke” cat.
  • Lastly, fever coat is a thing that can be observed in kittens; it occurs when the mama cat had a fever or was highly stressed in pregnancy, making the newborn kittens’ fur silver-type (silver, cream, or light reddish) rather than what their pattern “should” be. At a few weeks, the pattern that their genetics say they should have will establish itself.

Fur Length

Basically, the dominant gene L gives short hair and one of four recessive genes which all get the letter l gives long if a cat gets two copies of it. There’s one widespread variant of l which is the form that causes long hair in most cats, and then one l variant each for Maine Coons, Norwegian forest cats, and ragdolls.

Other genes affecting hair length and texture can be found but breeders consider them undesirable so they are not widespread. Many of them cause curly coats, or “rex” hair.

There are four genes which cause hairlessness. Only one, found in Russian Donskoy and Peterbald cats, is dominant; the other three, one found in sphinxes, one in British hairless cats, and the last in French hairless cats, are recessive.

A gene found in American Wirehair cats, Wh, causes “wiry, crinkly” fur.