The Siamese is an Asiatic Shorthaired cat in which colour is restricted to the points, ie, nose, ears, legs and tail, known as the Himalayan pattern or acromelanism. While colour mutations are present in other breeds, the Siamese is the only member of the Felidae family which naturally combines them in a delicate balance resulting in this striking contrast of coat pattern and colour.
The pattern, if not the personality, also occurs in mice, rabbits, hamsters and cavies. The Himalayan pattern has been acquired by Colourpoint Persians, Si-Rex, British, Ragdolls and Birmans, the last two exhibiting the white spotting gene which is anathema to the Siamese breeder. However, it is doubtful if any of these have the idiosyncrasies that make the Siamese cat so fascinating.
To understand how this unique pattern originated, and how it affects our Siamese, we should look at some simple genetics. Rare mistakes in the process of cell division, or the effects of radiation, can bring about minute chemical changes or variations in genes, known as mutations. These have given rise to the various coat colours and patterns we see in Siamese today.
In his book, Genetics for Cat Breeders Roy Robinson says "long ago...one of the first mutants to be found in the cat was probably that of self-black" which changed it from the wild tabby or agouti ticked coat.
The Himalayan pattern is caused by a semi-albino gene cs, which is a mutation of and a recessive to the gene for full colour C. It controls temperature gradients over the surface of the body and a greater loss of body heat from its extremities, which causes them to be darker than the body colour. Pointed kittens are born white-colour is undeveloped because the kittens were kept warm in utero, and begins to show on the coldest parts of the bodies, ie, the points, as they get older. The warmer areas of the body will develop little colour.
The normal gene C for "full colour" causes the black and orange pigment to be produced at full strength as seen in Oriental Cats, which are identical in type to Siamese but solid-coated, with green eyes. The mechanism of the Siamese gene cs belongs to the albino series which actually removes pigment. In the series of albino genes shown below in the order of dominance, cs is just above the gene for albino, or complete absence of colour. These alleles are named for the breeds characteristic of them, as follows:
C - Full Colour
cb - Burmese
cs - Siamese
ca - Blue-eyed albino
c - Pink-eyed albino
Roy Robinson writes that each of these alleles has a different effect upon skin and coat colour. With cb the black pigment (eumelanin) is changed to dark sepia of the Burmese. The adult Burmese has points which are only slightly darker than its body; in kittens, these are more obvious. The cb gene is incompletely dominant to cs and the various alleles cause a progressive biochemical degrading of pigment quality.
With cs, the seal brown is completely restricted to the points, the body fur being cream or pale fawn, varying in tone, as seen in our Seal Point Siamese. The eyes are partially deficient in pigment, but sufficient remains in the iris to produce the characteristic blue colour.
A proven spontaneous mutation occurred which changed black(B) to chocolate brown (b) - no outcross was used to produce the Chocolate Point Siamese. Another mutation created less intense (or more pale) colour called the Maltese mutation, or dilution gene (d). This gene acts by clumping elongate or spheroid eumelanin particles into irregular groups, causing greatly decreased light absorption, so that we visualise the colour of the fur as diluted, as in Blue and Lilac Points.
| Eumelanine Granule | Gene | Shape | Modifier & Distribution | Phenotype | Genotype |
|---|---|---|---|---|---|
| BLACK | B dominant wild type | elongate | D dispersed | Seal Point | aaB-cscsD- |
| BLACK | B dominant wild type | elongate | d clumped | Blue Point | aaB-cscsdd |
| chocolate brown | b recessive mutant | spheroid | D dispersed | Choc Point | aabbcscsD- |
| chocolate brown | b recessive mutant | spheroid | d clumped | Lilac Point | aabbcscsdd |
When the agouti gene is present with the Himalayan gene we get a Tabby Point, and where it is paired with the gene for solid-coloured coat, we get an Oriental with a Tabby Pattern. The Tabby or Lynx Point is a manufactured breed, originally developed by the mis-mating of a Siamese to a Tabby Domestic.
The gene cs not only causes the reduction of eumelanin (creating the Siamese pattern) but also tries to eliminate the phaeomelanin (or red pigment) which varies from green to yellow, to shades of orange to red. The red pigment and the Siamese pattern are, therefore, in direct conflict. Add to this the fact that the red pigment allows the latent tabby pattern to be partly visible and you can see that, because of its genetic make up, a perfect red point is almost the impossible dream.
When breeders experimentally created the first Red Points, they may not have realised that one biochemical system was pitted against another - something Mother Nature would never do. Nature always puts together systems, which interact harmoniously and efficiently; not systems, which compete, to the possible detriment of one another. Humans, in their arrogance, think they can go one better than Nature and do things the hard way.
Various factors, both genetic and environmental can affect the colour of the Siamese cat. As the points and body colour are temperature sensitive, an important factor in the depth of pigmentation is the amount of heat loss from the skin. Colour is affected by climatic conditions, for instance in Australia the Northern Territory's hot climate has a dramatic effect on Seal Point Siamese, whose points become brindled, with cream and seal hairs intermingling. In contrast , studs and other cats kept in an outdoor cattery in Tasmania's winter cold, have dense seal points and are darker in the body.
Theoretically, if we keep our Siamese warm, especially Seal Points, the lighter their body colour should be. But not too warm, as an elevation in temperature can cause brindling, or loss of pigmentation in the points; often seen after the cat has been ill. Siamese grow out darker on the body after surgery, and white hairs can appear on the points when the follicles are damaged. Age is another factor, and the sites of intense pigmentation appear on the shoulders and hips where the skin is closest to the underlying bone structure. The lighter the colour the more sensitive to heat - Chocolate is more sensitive to heat than Seal (Black) - hence the difficulty in breeding a Chocolate Point with perfectly even points.
That temperature alone effects colour is an over-simplification as there are many other genetic factors, including modifiers and polygenes. When visiting theLindisfarne Cattery in Auckland, New Zealand in 1964, I saw the UK import Spotlight Pride, who at 15 years old had a clear cream coat and dense seal points. In stark contrast, their other male Morris Maestro, also IMP UK, was extremely dark all over - almost a self-seal. Both studs were housed under identical conditions, so their disparity of colour must have been genetic.
Many years ago, the U.K. breeder Thetis Rendall, of Misselfore fame, set out to improve the colour in her Blue Points. For several generations she had to sacrifice type to achieve the desired glacial white coats and soft, pastel blue points described in the standard. There is no doubt that generations of selective breeding can establish the beautiful pale coat and correct points colour in a bloodline - while one wrong outcross can destroy it.
My personal theory is that Siamese with clear coats have the ticked tabby pattern in their genotype, which of course is invisible. Those with body markings and patches, to a greater or lesser degree, on shoulders, hips, flanks, stifle, belly, or groin, have mackerel or blotched tabby patterns. Fortunately we are given a clue, as kittens briefly show ghosting between 2-4 weeks and this is how I selected my Benwell Seal Points for good colour - they were well known for their cream coats.
I have deliberately not gone into the dilutes in depth and it will be very interesting when the Cinnamon, Fawn, and Caramel colours are recognised. In my opinion, these colours have been appearing for several years, and some cats, which have been penalised for non-conformity of colour, may need to be reclassified. This, along with type, is the subject of other articles.
Those of is who have "been around for a while' can remember when Seals and Blues conformed to the Standard. When I was breeding Seal Points in 1960, the coat was described as 'Cream shading to warm fawn'. The wording of the Standard has not changed but, alas, in many Seals seen on the bench today the colour has deteriorated to a muddy, sometimes cold, brown. There are Blue Points with dark steely-grey points and fawn coats, Chocolate Points that look like Seals, and 'off colour' Lilac Points. The distinctive contrast and beautiful clear colour that is the hallmark of the Siamese must be preserved at all costs, as without it they are in danger of becoming self-coloured cats.
It can be argued that the Himalayan pattern alone makes a Siamese. However, when this unique pattern is seen on a wicked, wedge-shaped face topped with 'bat' ears, set with brilliant sapphire almond-shaped eyes, combined with long graceful body and legs, an expressive whip-like tail, a voice that could shatter glass, insatiable curiosity, determination, capriciousness, remarkable intelligence, unswerving devotion, and a wonderful sense of fun - now that's what makes a stunning cat and a captivating companion.
