The colourpoint (pointed) pattern of the Siamese cat is a form of albinism. It is called the ‘Siamese pattern’ but I think technically it is better described as the “Himalayan pattern” or “Himalayan albinism”. We see this in a number of different species of animals including rabbits and goats from the Himalayan region which is north of India.
Kittens are born devoid of pigment in the hair strands. The kitten then begins to form pigment on the nose and ears within a few days. This is due to the presence of the albinism allele. The word “allele” refers to each of two or more alternative forms of a gene that arises by mutation and found at the same place on a chromosome.
So, we have a genetic mutation which interrupts the production of melanin (the pigment) by the pigment producing cells called melanocytes in the skin. This mutation inhibits the production of pigmentation in the warmest areas of the body. In other words, the production of pigmentation is temperature-sensitive.
As a result, the cooler areas of the body such as the legs and head display pigmentation while the trunk of the body has reduced pigmentation. This provides the pointed appearance, as they call it in the cat fancy.
And, of course, the unborn kitten is at the body temperature of their mother which is cosily warm (99.5º-102.5º Fahrenheit which is about 38º Celsius). And therefore, the production of pigment by the kitten in the womb is inhibited and being inhibited it leaves the kitten looking white because inside the hair strands there is no melanin pigment.
When the kitten is born the ambient temperature changes their appearance as the genetic mutation takes control of the production of pigment.
The Siamese allele, as it is called, has the following symbol: cs used by geneticists. The albinism allele has other effects on the Siamese cat such as disrupting the visual pathway which it is said prevents the cat from having full binocular vision. Siamese cats compensate for this abnormality which causes cross wiring from eye to brain. You will see the typical Siamese cat squint. It is believed that Siamese cat see normally nonetheless.
The classic pointing is ‘seal’ pointing which is a dark brown or black pigment which is the melanin. Selective breeding in the cat fancy has created a range of colours for the points i.e. the extremities of the cat and one such colour is called blue which is a kind of gray/blue which in turn is a diluted black. I guess they introduced the dilution gene into the cat to dilute the melanin pigmentation.
Two other points are making: older cats have poorer circulation and therefore their flanks are darker. Also, a Siamese cat in Iceland that is allowed to go outside is going to be whiter than a Siamese cat in Indonesia because the ambient temperature affects the production of pigment.
This concludes the article.
What follows is in addition to the article and is not strictly relevant to answering the question.
Many early Siamese had kinked tails and both this “defect” and the Siamese cat squint have been selectively bred out of this cat. In some ways breeding out the kinked tale is rather sad because this is part of the inheritance of the Siamese cat and you see pointed cats in the Far East with shortened and kinked tails.
Personally, I would also add that it is sad that the American cat fancy has seen fit to create the extreme Siamese cat or what I call the modern Siamese cat which is too slender and the face too elongated (rat face). It’s a face which is at the opposite end of the spectrum to the Persian cat (far too flat). There is no need to breed cats to extreme like this. The modern Siamese cat looks unnatural but there is a natural tendency for humans to go too far.
The first Siamese cat fanciers club was founded in Britain in 1902 and the Siamese Cat Society of America was founded in 1909. I have a good friend whose wife is Thai. You probably know that Thailand was formerly called Siam and Siam is where the original Siamese cats came from.
I asked her whether she ever sees Siamese cats in Thailand and she said no. You just don’t see Siamese cats in Thailand! You would have thought that they would be everywhere, this being the home of the Siamese cat. But apparently not. Siamese cats were said to be the companions of royalty in Thailand but there is some disagreement about this.
To the best of my knowledge and based upon research, the first Siamese cats in the Western world were acquired by Mrs Vyvyan living in Dover, England, UK. She brought Siamese cats to her home in 1886. She said that the cats were very affectionate and did not like to be left alone. They followed her from room to room like dogs. And we know that Siamese cats are famous for their loyalty to their human companion.
She also said that they are very strong and they fight with strange dogs! She said that Siamese cats “conquer all other than tomcats in their neighbourhood”. I have a full article on this lady and her acquisition of the first Siamese cats in the Western world which you can read by clicking on this link if you wish.
Below are some more articles on Siamese cats.