College of Cat Genetics: Student Seminar 3
by Patricia Turner
A number of students have expressed puzzlement over the inheritance of colours which are not produced by the action of one single gene. Such a colour is lilac or lavender. Contrary to popular belief, there is no gene for lilac--it is a colour effect produced by the combination of genes for chocolate brown and dilution. Thus, the term carrying lilac seen in some advertisements is meaningless. A cat may carry (be heterozygous for) brown, it may carry dilution or it may carry brown AND dilution. When two cats combining the genes for both brown and dilution combine, they can produce the Lilac. Lilac is bbdd, thus a double recessive.
The way in which one colour gene can work upon another is intriguing and not always as one might expect. If a painter were to mix brown with blue he would not get a colour with a paler tone. If he were to mix orange with brown and blue, he would not get cream. So it is better to forget such comparisons and rely instead upon knowledge of the colours produced by similar gene mixtures in other species. If this knowledge is not available, then the only way to establish the truth is by observations on kittens produced from test matings. I do not call such matings experimental as this word suggests the random mating of two unalike cats to the average breeder.
When brown/dilution (producing lilac) is added to agouti cats, the colour undergoes yet another change. The action of the agouti gene is to produce areas of the hair that are banded in black and yellow pigment. The allocation of the agouti hair areas is controlled by another gene known as tabby pattern and, although the differences in tabby pattern are interesting, they are not particularly relevant to the point of this article. When brown is added, the black becomes chocolate brown and the yellow becomes a warm orange-red. When dilution is also added, the chocolate brown becomes lilac and the orange-red becomes a more beige-fawn. Thus, in the normal agouti, there are definite areas of dark and light tone in each hair; in the chocolate agouti the differences are less and in the lilac agouti the differences are so small as to go almost unremarked, the tone of the beige areas being almost similar to the tone of the lilac.
I mentioned earlier that the differences in tabby pattern are relevant to this article but the one exception is the difference produced by the presence of the Abyssinian tabby pattern gene on the Lilac agouti. The Abyssinian pattern produces a cat with the agouti hairs extending over almost all the body and the more solid colour areas restricted to the spine line and tail. With agouti hairs coloured in lilac and beige bands of almost identical tone, the cat appears fawn or beige and not lilac at all. Thus, in this instance, the beige colour is produced by the mixture of Abyssinian tabby pattern, agouti, chocolate brown and dilution. This is the cat now recognized by the British GCCF as Cream Abyssinian (North American Fawn Abyssinian). Admittedly, the GCCF also recognizes the Lilac Abyssinian but these are, in fact, two names for the same cat. Differences between the coat colour of cream or lilac Abyssinians can be accounted for by the differences between the colours of chocolate brown.