| This is taken from Feline Husbandry by Niels C. Peterson:
Silver, Tipped and Smoke: In the Silver, the yellow-gray agouti
component of the tabby is absent, creating the superficial illusion of
an off-white cat with black Tabby markings. These cats may have any of
the 3 Tabby patterns, of which the blotch or classic is probably the
most outstanding. Breeders have selected for a clear white background
color and solid Tabby markings to realize maximum contrast. The Silver
phenotype is produced by the I allele, and the genotypes are IITT
(striped or "mackerel"),IItbtb (blotched "classic") and IITaTa
(Abysinian). The I gene inhibits pigment in the hair t a variable
degree. The silver may be regarded as the minimum degree of
inhibition. The inhibition may be more pronounced, giving rise to the
shaded silver. Such cats have obvious white undercoats and rarely
discernable tabby markings. The most extreme expression is the tipped
or "chinchilla". In these animals, only the tip of the hair is
pigmented and the tabby markings are not discernable.
The effectiviness of the I gene in eliminating pigment is due in part
to the fact that the silver and tipped breeds are agouti. When the I
gene is combined with the non-agouti, the reduction is significantly
less. In fact, all of the hairs are now distally pigmented and not
merely the tabby pattern hairs, as in the silver tabby. These aaII
indiviuals are known as Smoke. The expression of light undercolor
varies from indistinguishable, from the slate blue of the normal
nonagouti (aa), to light blue and finally white. There are several
cases on record of black cats breeding as Smokes. These are almost
certainly instances of very dark Smokes.
The Silver tabby, shaded Silver, Tipped (chinchilla) and Smoke
phenotypes may be combined with b, d and O alleles to produce the usual
range of colors. These have been expoited in the oriental group of
breeds to establish phenotypes not recognized by the traditional
breeds. The Silver tabby, shaded Silver and Tipped varieties have
identical genotypes, differing only in the expression of I. The
expression of the I gene is probably governed in part by modifying
polygenes.
Hope this helps someone!
Karen
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