This page simply lists the symbols for commonly referenced genes for colours, patterns and anomalies. Where there are several alleles, these are listed in order of dominance (some are co-dominant) though the order of dominance for posited genes is unknown. Although most of the traits/genes listed here are shown as dominant/recessive, some traits once thought to be controlled by simple Mendelian inheritance principles are actually influenced by one or more modifier genes.

Some genes are hypothetical or under debate i.e. an effect has been observed, but the existence of a single gene governing that effect has not been proven.

There are two types of colour pigment - eumelanin (black/brown pigment) and phaeomelanin (yellow/red pigment). There are several mutant forms of the black/brown pigment. The coat colour depends on which pigments are present. A number of other genes modify the amount of pigment in the hair shaft and whether it is laid down in alternating light and dark bands along the shaft or as a single, solid band stretching from follicle to hair tip. At the foot of this page there is a more detailed description of how melanin works to give a wide array of colours.

These are genes that modify the action of other genes giving more subtle variations on the basic colour. Although it could be argued that dense/dilute modifies the colour, it is listed as a basic colour.

Colourpoint is not included here as it is a form of albinism. These genes affect the distribution of colour on the body. Some of the posited genes have been given symbols by breeders, but are not widely accepted. You will find that outdated texts give Ta as ticked tabby, Tm as mackerel tabby and Tc as classic tabby and describe them as alleles of a single "tabby" gene. This was later proved incorrect. Tm and Tc are no longer used; mackerel is now Mc and classic tabby is mc. Ticked tabby is a different gene and remains Ta although some early research designated it U for "unstriped tabby".

These are fur type anomalies that are (or have been) selectively bred; some of the newer ones have not been allocated symbols. At the time of writing there are also several "new" rexes whose genetic make-up has not yet been determined.

These are conformation anomalies that are selectively bred.

 ABNORMALITIES

This list excludes those abnormalities that have been developed as breed traits. The list includes both physical and physiological anomalies.

Colour is caused by the melanin pigment. There are two distinct types of melanin in the cat: eumelanin (black-based) and phaeomelanin (red/yellow-based). Eumelanin is, in the absence of colour modifer genes, black or dark brown (seal). Phaeomelanin is, in the absence of colour modifer genes, a yellowish/orangey colour known to cat fanciers as "red". Melanin is deposited on the hair shaft as the hair grows, but is not deposited at a constant rate. This results in the darker tips frequently seen on hairs. The Agouti protein affects the deposition of melanin in the growing hair and results in the banding effect (several bands of dark and light along the hair shaft). It causes alternating, distinct bands of eumelanin (black/brown) and phaeomelanin (red/yellow).

The mutant "Non-Agouti" form of the Agouti protein inhibits the banding effect and results in solid coloured hairs or hairs. The Tabby pattern genes inhibits the action of the Agouti gene in certain areas of the coat resulting in some agouti areas (ticked background colour) and some non-agouti areas (pattern). Sex-linked Red replaces the eumelanin in the growing hairs with phaeomelanin - the hairs are still ticked, but the bands of colour are light and dark red. Unlike eumelanin, phaeomelanin pigment is not greatly inhibited by the Non-Agouti protein hence red cats always show a tabby pattern.

Tortoiseshell cats have a patchwork effect; some areas of the coat have eumelanin while other areas have phaeomelanin. The eumelanistic areas are affected by tabby, non-agouti etc, but the phaeomelanin areas are not. As a result, the tabby pattern still shows up on the red areas regardless of whether the cat is a tortie or a tabby-tortie. A series of "rufous polygenes" affect the richness of the red colour - ranging from yellow-orange through to rich orange-red.

The B (black/brown) gene has a lightening effect on eumelanin. Depending on which of the B genes a cat has, the coat can be black/brown, chocolate or cinnamon. The D (dense/dilute) gene affects the density of pigment in the hair and affects both eumelanin and phaeomelanin. The effect is a washed out version of the original colour e.g. black becomes blue, red becomes cream. The Dm (dilute modifier) gene only affects the colour if the cats are already dilute (homozygous for the dilution gene). It "browns" or "caramelises" the diluted colour e.g. blue becomes caramel, cream becomes apricot.

The C (full colour) gene comes in various flavours and causes different types of albino. Not all albinos are pure white! The C gene affects the intensity of melanin production. The normal (dominant form) is "full colour". The mutant forms affect the colour intensity and are temperature sensitive - the higher the temperature, the more effective they are. C^b is the Burmese factor and is only slightly temperature sensitive; it causes a slight lightening of black (eumelanin) to brown (sable) and of orange (phaeomelanin) to a yellow colour. C^s is the Siamese factor and is much more temperature sensitive; it has a much greater lightening effect than the Burmese factor causing greater contrast between the body colour and the points. Cats that have one copy of the Burmese factor and one copy of the Siamese factor show an intermediate effect known as Tonkinese. The most recessive form is c which is the rare pink-eyed albino totally lacking in pigment. C^a is the blue-eyed albino where there is a very small amount of pigment.

Robinson's Genetics for Cat Breeders. This is currently in its 4th Edition (1999) and is the cat breeder's bible. However, further genes and a lot more mutations have been identified since it was published in 1999 and an updated version is eagerly awaited.