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from gloria stephens

gloria stephens stephens at hq.jcic.org
Sat Jul 22 11:07:10 EST 1995

Tabby genes are in the genotype in all domestic felines.
For the tabby pattern to be seen at its best, the Agouti gene must be 
present;is dominan. Its recessive, nonagouti, is responsible for the 
solid colored hair shafts.
The gene for full color pigmentation is located at the Albino locus, and 
the recessives for diminished pigmentation areat thatlocus.

A = agouti, a\a = non agouti
B\- = black, b\b=chocolate, b(l)\b(l)=cinnamon
T(a)\ = Agouti tabby
T = Mackerel tabby
t(b)\t(b) = classic tabby
C\- = full color,
c(b)\c(b) = sepia or Burmese coloring
c(s)\c(s) = pointed coloring

The genotype for the tabby (I am leaving out the dense pigmentation, 
white spotting, silver etc genes) would be

A\-, B\-, C\-, T(a tabby pattern)

The genotype for the solid colored Siamese is:

a\a,  B\-, c(s)\c(s), T(a tabby pattern)

If the tabby is homozygous for Agouti (A\A), all kittens are tabby.

If the tabby is heterozygous for Agouti (A\a), then some of the kittens 
MAY be solid.

To say that one will always gave a certain percentage of kittens born 
'solid' is, IMO, impossible. 

In the solid black, the eumelanin is there, nothing to change it. In the 
Siamese, the eumelanin is there, but the pointed gene (thermolible) form 
of tyrosinase has allowed altered pigmentation to develop on the coldest 
part of the body - the points. Eye color also is changed, in that there 
is no pigmente deposited in the front of the iris, therefore, the light 
that is reflected back - is blue. 

Gloria Stephens

mgk at darwin.clas.Virginia.EDU (Mahlon G. Kelly) wrote:
>Re. feline genetics. I have noticed that a cross betwen a tabby
>and a pure-bred siamese will produce more than 1/2 50% pure
>black kittens, and they preserve their black pigmentation until
>old age, when a few white hairs and white wiskwas (cat spelling
>for vibrisae) will appear. 
>Several vets have confirmed that they have seen the same.
>Purebred Siamese breeders deny it. "MY cats breed with a tabby?
>Don't be rediculous". At any rate, is there any genetic basis
>for this? I find that the literature on cat genetics is sparse
>indeed. It is mostly anecdotal, and could have been written
>before Mendel.
>Associate Professor (Emeritus)
>University of Virginia
>mgk at darwin.clas.virginia.edu

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