Cat Genetics

White Cats

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There's a catch to owning a white cat; these cats have a higher chance at having skin cancer or being deaf. But, it's a common mistake to mistake white spotting or white masking on a cat with an actual white cat, so that's what I'll be talking about.

The white masking gene, W/w. The "W" gene prevents the normal replication and migration of pigment-producing cells during embryologic development. As a result, WW and Ww cats have a greatly reduced number of melanocytes and appear white, no matter what other color genes it may carry. Only a cat that is homozygous recessive (ww) will express normal pigmentation. Thus, W is epistatic to the other coat pigmentation genes. Some cats with the W allele of this gene are deaf and/or have depigmentation of the iris of one or both eyes, resulting in blue eye color.

The white spotting or piebald spotting gene, S/s, has variable expression, so that an SS cat often has more extensive white patching than an Ss cat. It is this gene that creates the familiar white blaze across the face, a white bib, tuxedo pattern, or dappled paws. A hypothetical Sb allele ("gloving gene") may cause the mittens in Birman and Snowshoe breeds. Some researchers believe that there are separate white spotting genes for distinct forms of white pattern, such as the white locket that some cats have on their neck or bellies.

The cat displays several distinctive white pigmentation phenotypes that have been under selection by cat fanciers: Dominant White, uniform white coat, often accompanied by blue irises and deafness, white spotting (or piebald): variable distribution of white areas on the body, and gloving: white pigmentation restricted to the paws. Albinism, the complete absence of pigment, is known to be caused by a distinct locus from White, called "C".

The dominant white gene is associated with developmental defects where melanocytes fail to migrate to the skin during embryologic development. The number of melanocytes are greatly reduced, but not always absent (hence temporary smudges of colour on the heads of some kittens). This can result in one or both blue eyes and in degenerative changes of the ear resulting in partial or total deafness.

Dominant white (W) masks other colour and pattern alleles hence solid white cats may genetically be solid or patterned cats in any colour. The underlying colour will show up in any offspring that don't inherit the Dominant white allele.

The white spotting gene (S) creates white markings on a solid or patterned cat. The white spotting gene is variable in expression from white locket (face/ paws/legs/white stomach) through to solid white covering 40-60 % of the body to high grade spotting (van pattern) where most of the body is white, other than the head and tail that can resemble dominantno white, however it is rarely associated with deafness. Homozygosity vs heterozygosity for the ws allele appears to have an influence on the degree of white pigmentation.

A separate recessive gene (G) has been identified for Birman white gloving. There are hypothetical genes for other white mitted patterns and for the York Chocolate white pattern. There are believed to be genes, as yet unidentified, for the white throat locket and white brisket spots.