College of Cat Genetics
by Patricia Turner
In Study Unit 6 I referred to the gene for dilution which converts black or seal to blue, red to cream, and chocolate to lilac. This has puzzled one reader who had previously believed the dilution gene to be that which converts black to brown. He had been under the impression that the gene as I described is that known as the blue gene and asked for clarification.
This problem is one of terminology. The colour gene known as the dilution gene is one affecting the intensity of coat and eye colour by clumping the pigment granules but not, as in the alleles of the albino series, decreasing the number of granules secreted. When dilution is present, the granules are concentrated into irregular groups so that light absorption is affected and black fur looks grey or blue. If the fur has already been affected by a gene at another locus then the clumping will still take place but the final effect will differ in accordance with the original coat colour. When the cat already owns two genes for brown, the clumping caused by dilution gives the lilac colour effect and, when the cat owns one or two genes for red the clumping gives the cream colour effect. Thus dilution and blue are one and the same if we are discussing the differences between black and blue cats. But if we are concerned with chocolate brown and lilac cats or with red and cream cats a reference to blue may be misleading.
As one concerned actively in genetic research, I have been careful to use only terms that are accepted terminology in scientific circles and to avoid the use of slang names sometimes used by fanciers. By this means, the information I give should be intelligible to all English speaking breeders. The name used internationally for the gene producing blue on black, cream on red and lilac on chocolate is dilution. It is inherited as a simple recessive and its alternative is full intensity of colour.
Full Intensity of Colour (D) Dilution (d) Black Blue Seal Point Blue Point Chocolate Brown Lilac or Lavender Chocolate Point Lilac or Frost Point Red Cream Red or Flame Point Cream Point
The brown gene, on the other hand, is not a gene concerned with dilution by clumping. In fact, it works on the protein framework of the melanin granule itself affecting both its colour and shape. The brown gene also affects eye colour. So the picture of a black cat is one of normally shaped black pigment granules: when dilution acts upon these they retain their colour and shape but clump into groups giving the effect of blue. When the gene for brown acts upon the normal black granules they are altered both in colour and shape but do not clump. If the cat has both brown and dilution active it is lavender or lilac and has brown pigment granules which are clumped into groups. Technically it is incorrect to describe brown as a dilution. It is symbolized as b with its alternative being B.
A full description of the dilution and brown genes can be found in The Comparative Genetics of Coat Colour In Mammals by A.G. Searle, published 1968 by Logos Press & Academic Press. Further details of the effects of these genes in the Siamese breeds are to be found in the forthcoming Encyclopedia of the Siamese Cat by Mary Dunnill, published by Pelham Books. Breeding charts for all colours of Siamese are given in the section on genetics. Other references can be found in Genetics for Cat Breeders by Roy Robinson, published by Pergammon, and in The Biology of the Laboratory Mouse, 2nd Edition, published by McGraw-Hill, New York.
The second part of this seminar should deal with what are described as neither-nors. It seems that this term is in common usage among the cat fancy writers in the USA but, as an Englishwoman, I admit defeat. I am unable to comment on neither-nors for the simple reason that I do not know what they are! The reader went on in her letter to state that she had been advised against breeding Seal Point Siamese to Chocolate Points and Blue Point Siamese to Lilac Points and, in some way, the neither-nors appear to be associated with these statements. I can certainly comment on this point.
Generally speaking, Siamese breeders are in agreement over the desired points and coat colour of the Seal Point. A good Seal Point in one state or country is probably acceptable as a good Seal Point in another. Thus breeders of Seal Points tend to select their breeding stock with a common ideal in mind. Unfortunately this situation is not so apparent in other colours. The older breeders bemoan the loss of the true milk chocolate point Siamese and, while some judges may describe a Chocolate point as nearly ginger, others may write of the same cat: a full, rich, true chocolate. The differences in chocolate point coloration are partly due to polygenes (small genes with additive effect) for a quality known as rufism, although there are also grounds for belief that another major gene may also be involved. Blue Points also vary, although less markedly than Chocolates, while the differences in Lilac Points are so noticeable that a successful cat in some European countries would be considered quite incorrect in other parts of the world.
The road to success for a specialist breeder is, therefore, a breeding programme involving selection towards the colouration considered the ideal in his cat fancy community and the simplest method of selection is one where all the kittens considered are of the same point colour. If a breeder likes milk chocolate and pink-lilac and breeds with both ideals in mind, he may well obtain a proportion of plain chocolate and blue lilac in his litters.
There are reasons behind the often-given advice to specialize within one point colour; for the novice or the small breeder the advice is often worth consideration. It is certainly better advice than the suggestion to breed dark-coated Seals to Lilac Points in order to get more contrast. The fact that the Lilac is generally a lighter cat does not ensure the retention of lightness in the coat in its Seal Point progeny.
However, there are other considerations than those of colour. More important than anything else are the considerations of health, vitality, fertility and general viability. If these are considered poor in any one colour group, then the best advice of all would be to mate to cats of another colour where better qualities are reported. Rather a healthy mixed litter than a perfect litter of show quality Seals (or Blues, Chocs, Lilacs, etc.) with poor stamina.
When I started breeding Siamese, I had a Lilac Point that was too blue, a Chocolate Point that was too dark and a Blue Point that was too fawn. Only by selection did I achieve improvement and, to help me, I used the method known as The Total Score Method of selection. Once I had more knowledge of breeding and embarked on the making of new varieties, I was able to combine the use of the Total Score Method with manipulation of coat colour genes to achieve the successes I have had with my Foreign Whites and other Orientals. Although, at that time, I was concerned primarily with shorthairs and Siamese, a basic knowledge of the inheritance of the major genes, together with the use of the Total Score Method of selection are all that any breeder of any variety needs to achieve improvement if his care and management are of a good standard. The Total Score Method is very well described in Roy Robinson's Genetics for Cat Breeders and will be the study if a Study Unit later in the series College of Cat Genetics.
New Siamese Varieties
The final point I wish to cover in this seminar is one concerned with the term non-allelism. If a gene is described as allelic to another, then it can be regarded as its alternative. For example, black is allelic to dilution and thus a cat may be either black or dilute. But, if two genes are non-allelic, they are not alternatives and this fact accounts for the Smoked Siamese reported in the article by Roy Robinson and myself. The opinion held on Smokes and Siamese was that they were alternatives and that one could not have a cat that was noth Smoke and Siamese. But the appearance of Scintilla Smoke Signal, a smoked Seal Point Siamese changed all that. The fact that more kittens followed in the same image proved the point: the gene producing smoke is not an alternative or an allele of Siamese. Thus it is described as non-allelic. In fact, this has opened the way for a host of new Siamese varieties, the most striking of these to date being the Silvered Chocolate Tabby Point.