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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