Your Pet Guide

Colorpoint

The colorpoint pattern is most commonly associated with Siamese cats, but may also appear in any domesticated cat. A colorpointed cat has dark colors on the face, ears, feet, and tail, with a lighter version of the same color on the rest of the body, and possibly some white.



The exact name of the colorpoint pattern depends on the actual color, so there are seal points (dark brown), chocolate points (warm lighter brown), blue points (dark gray), lilac or frost points (silvery gray-pink), red or flame points (orange), and tortie (tortoiseshell mottling) points, among others.

This pattern is the result of a temperature sensitive mutation in one of the enzymes in the metabolic pathway from tyrosine to pigment, such as melanin; thus, little or no pigment is produced except in the extremities or points where the skin is slightly cooler.

For this reason, colorpointed cats tend to darken with age as bodily temperature drops; also, the fur over a significant injury may sometimes darken or lighten as a result of temperature change. The tyrosine pathway also produces neurotransmitters, thus mutations in the early parts of that pathway may affect not only pigment, but also neurological development.

This results in a higher frequency of cross-eyes among colorpointed cats, as well as the high frequency of cross-eyes in white tigers.

White cats

True albinism (a mutation of the tyrosinase gene) is quite rare in cats. Much more common is the appearance of white coat color due to a lack of melanocytes in the skin. A higher frequency of deafness in white cats is due to a reduction in the population and survival of melanoblast stem cells, which in addition to creating pigment producing cells, develop into a variety of neurological cell types. White cats with one or two blue eyes have a particularly high likelihood of being deaf.

Smoke cats

The bottom eighth of each hair is white or creamy-white, with the rest of the hair being a solid color. Genetically this color is a non-agouti cat with the dominant inhibitor gene; a non-agouti version of the silver tabby. Smoke cats will look solid colored until they move, when the white undercoat becomes apparent. It is mostly found in pedigreed cats (especially longhair breeds) but also present in some domestic longhaired cats.

The domesticated cat and its closest wild ancestor are both diploid organisms that possess 38 chromosomes and roughly 20,000 genes. About 250 heritable genetic disorders have been identified in cats, many similar to human inborn errors.

The high level of similarity among the metabolisms of mammals allows many of these feline diseases to be diagnosed using genetic tests that were originally developed for use in humans, as well as the use of cats in the study of the human diseases.

An interesting example of a mutation that is shared among all felines, including the big cats, is a mutant chemosensor in their taste buds that prevents them from tasting sweetness, which may explain their indifference to fruits, berries, and other sugary foods. In some breeds of cats congenital deafness is very common, with most white cats (but not albinos) being affected, particularly if they also have blue eyes.

The genes responsible for this defect are unknown, but the disease is studied in the hope that it may shed light on the causes of hereditary deafness in humans. Since a large variety of different coat patterns exist within the various cat breeds, the cat is an excellent animal to study the coat genetics of hair growth and coloration.

Several genes interact to produce cats' hair color and coat patterns. Different combinations of these genes give different phenotypes. For example, the enzyme tyrosinase is needed to produce the dark pigment melanin and Burmese cats have a mutant form that is only active at low temperatures, resulting in color appearing only on the cooler ears, tail and paws.

A completely inactive gene for tyrosinase is found in albino cats, which therefore lack all pigment. Hair length is determined by the gene for fibroblast growth factor 5, with inactive copies of this gene causing long hair.

The Cat Genome Project, sponsored by the Laboratory of Genomic Diversity at the U.S. National Cancer Institute Frederick Cancer Research and Development Center in Frederick, Maryland, aims to help the development of the cat as an animal model for human hereditary and infectious diseases, as well as contributing to the understanding of the evolution of mammals.

This effort led to the publication in 2007 of an initial draft of the genome of a Abyssinian cat called Cinnamon. The existence of a draft genome has led to the discovery of several cat disease genes, and even allowed the development of cat genetic fingerprinting for use in forensics.