Point coloration refers to animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and (in males) scrotum. It is most recognized as the coloration of Siamese and other breeds of cat, but can be found in rabbits as well. Point coloration is a form of partial albinism resulting from a mutation in tyrosinase, an enzyme involved with 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.[1] As a result, dark pigment is limited to the coldest areas of the body, that is, the extremities. Pointed kittens are born white, since there is little temperature difference in the womb. As the kitten ages, the cooler areas darken while warmer areas remain cream to white in color. Points are not limited to solid colors or dark colors. It is possible to have a red (orange color) or fawn (pale warm gray) point. It is also possible to have a tortoiseshell or tabby point. If the points are not black or at least very dark, the coloration is called colorpoints. Because of this restriction of pigment, pointed cat's eyes are always some shade of blue, because the top layer of the iris is not covered in another color, letting the blue show through. The back of the eye also lacks pigment, giving these cat's pupils an eerie red reflection in the dark, unlike a normally pigmented cat's green to blue shine. The point gene is carried on the C locus, where pure albinism is also carried. It is shown with the sign cs, and needs two alleles of cs for the points to be expressed. The point gene is recessive to the tabby gene. Also carried on the C locus is the gene for the sepia pattern. This is the darkest of all of the pigment restricting patterns, and pigment is only paled at the warmest point in the body, the abdomen. This pattern's gene is represented by cb. When a cat carries the genes cs and cb, the mink pattern is formed, in which the pigment distribution is between a sepia and a point cat.
Cat breeds with points
- Balinese
- Birman
- Colorpoint Shorthair
- Himalayan, also known as the Colourpoint Persian in Europe
- Javanese
- Snowshoe
- Tonkinese
- Siamese
- Ragdoll
Rabbit breeds with points
References
- ^ D. L. Imes et al. (April 2006). "Albinism in the domestic cat (Felis catus) is associated with a tyrosinase (TYR) mutation" (Short Communication). Animal Genetics 37 (2): 175. Retrieved on 2006-05-29.
