whitespotting
White Spotting Gene
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Julie Simpson
(Member NZCF Genetics Advisory Committee)

The white spotting gene is a highly variable, difficult to control gene, which produces white spotting randomly, with any colour and is therefore, a separate entity as such.

Major genes are those, which affect dominant and recessive traits, such as colour, pattern and coat type. Polygenes, are the many minor genes, which are responsible for the degree of white spotting, amongst other things. These cannot be manipulated individually, however by repeatedly selecting for desirable characteristics, they can be controlled to a degree.

Breeding cats with a low degree of white decreases the chances of getting cats with a high degree of white. By careful selection of breeding stock, Birmans selectively bred for many generations for a low degree of white can remarkably reproduce that degree with some consistency. The hybridisation of other cats with the Birman to produce the Ragdoll, has indicated that gloving can be lost very easily, with a whole new spectrum of the distribution of white being introduced.

To understand this process we need to look at how the white spotting gene works. Melanocyte or pigment producing cells are formed along the neural crest (spinal area)of the embryo these cells migrate down the sides to the feet, The presence of the white spotting gene halts the progress of melanocyte before it reachs the feet or undercarriage at maturition of the feotus, resulting in unpigmented or white areas typically found in Birmans.

While there has been much speculation regarding the gloving gene, with some thought that it is separate to that of the dominant white spotting gene (responsible for Bi-colour and Van patterns), there has been no conclusive evidence to support this theory.

The knowledge gained by experimental programmes involving crossing out to other breeds, to introduce new colours, has led to the belief that low grade white spotting is definitely carried as a recessive. First generations may lose the white spotting, when outcrossing but it is rapidly recovered in successive matings.

The white spotting in the Birman is not in fact confined to the feet, as most people believe. As with all low-grade white spotted cats, white is typically confined in varying degrees to the feet, abdomen, and chest, the Birman is no exception. Genetically, the Birman is a pointed, low grade Bi- colour as is the Mitted Ragdoll. In this Semi-albino series, white chest and abdomen spots can be difficult to identify, due to the fact that the immature coat of the pointed cat is pale and provides no contrast. On maturity as body toning increases these spots or patches become evident, varying in size to some degree with each individual.

The progression of white spotting typically results in the reduction of coloured areas and an increase in the white areas,.beginning with an increase up the legs , and increased patch sizes on the abdomen, chest, and chin.as seen below The final result, masking its original colour and pattern by producing the full expression of the white spotting that is a completely white cat.

The typical nose and chin involvement of white spotting, as seen in the domestic and ragdoll population with regularity has virtually been eliminated, by rigid selection within the Birman breed.
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References:
The Pigment Parade - Lorraine Shelton
Genetics for Cat Breeeders - Roy Robinson