Siamese (and Traditional Siamese or Applehead Siamese) basic information
All Siamese have a creamy base coat with coloured points on their muzzles, ears, paws and lower legs, tails and (in males) scrota. The pointed pattern is a form of partial albinism, resulting from a mutation in tyrosinase, an enzyme involved in melanin production. The mutated enzyme is heat-sensitive; it fails to work at normal body temperatures, but becomes active in cooler areas of the skin. This results in dark coloration in the coolest parts of the cat's body, including the extremities and the face, which is cooled by the passage of air through the sinuses. All Siamese kittens, although pure cream or white at birth, develop visible points in the first few months of life in colder parts of their body. By the time a kitten is four weeks old the points should be clearly distinguishable enough to recognise which colour they are. Siamese cats tend to darken with age, and generally adult Siamese living in warm climates have lighter coats than those in cool climates.
Originally Siamese all had seal (extremely dark brown, almost black) points, but occasionally Siamese were born with blue (gray) points, chocolate points, or lilac (pale gray) points, each of which was eventually accepted by the breed associations and allowed to compete in shows. Genetically, blue point is a dilution of seal point and lilac point a dilution of chocolate point, which is itself a variation of seal point. Later, outcrosses with other breeds developed Siamese cats with points in other cat colours and patterns including red point, lynx (tabby) point, and tortoise-shell ("tortie") point. In the United Kingdom, all pointed Siamese-style cats are considered to be part of the Siamese breed. In the United States, the major cat registry, the Cat Fanciers' Association, considers only the four original colorations as Siamese: seal point, blue point, chocolate point, and lilac point. Oriental cats with colorpoints in colors or patterns aside from these four are considered Colorpoint Shorthairs in the American cat fancy.
Siamese have almond-shaped, bright blue eyes and short, flat-lying coats. Many Siamese cats from Siam had a kink in their tails but over the years this traits has been considered to be a flaw and breeders have largely eradicated it. Many early Siamese were cross-eyed to compensate for the abnormal uncrossed wiring of the optic chiasm, which is produced by the same albino allele that produces coloured points. Like the kinked tails, the crossed eyes have been seen as a fault and through selective breeding, the trait is far less common today.