Cat Genetics

Fur Texture

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Cat fur length is governed by the Long hair gene in which the dominant form, L, codes for short hair, and the recessive l codes for long hair. In the longhaired cat, the transition from anagen (hair growth) to catagen (cessation of hair growth) is delayed due to this mutation. A rare recessive shorthair gene has been observed in some lines of Persian cat (silvers) where two longhaired parents have produced shorthaired offspring.

There have been many genes identified that result in unusual cat fur. These genes were discovered in random-bred cats and selected for. Some of the genes are in danger of going extinct because the cats are not sold beyond the region where the mutation originated or there is simply not enough demand for cats expressing the mutation.

In many breeds, coat gene mutations are unwelcome. An example is the rex allele which appeared in Maine Coons in the early 1990s. Rexes appeared in America, Germany and the UK, where one breeder caused consternation by calling them "Maine Waves". Two UK breeders did test mating which indicated that this was probably a new rex mutation and that it was recessive. The density of the hair was similar to normally coated Maine Coons, but consisted only of down type hairs with a normal down type helical curl, which varied as in normal down hairs. Whiskers were more curved, but not curly. Maine Coons do not have awn hairs, and after moulting, the rexes had a very thin coat.

There are various genes producing curly coated or "rex" cats. New types of rex pop up spontaneously in random-bred cats now and then. Here are some of the rex genes that breeders have selected for:

• r = Cornish Rex, recessive.

• gr (provisional) = German Rex, recessive. Same locus as Cornish, but proposed as a different allele. However, most breeders consider the German Rex to have r/r genotype.

• re = Devon Rex, recessive.

• ro = Oregon Rex (extinct), recessive.

• Se = Selkirk Rex, dominant although sometimes described as an incomplete dominant because the three possible allele pairings relate to three different phenotypes: heterozygous cats (Sese) may have a fuller coat that is preferred in the show ring, while homozygous cats (SeSe) may have a tighter curl and less coat volume. (sese type cats have a normal coat.) This phenomenon may also colloquially be referred to as additive dominance.

• Lp (provisional) = LaPerm, dominant: Lp/lp and Lp/Lp individuals have the same phenotype.

There are also genes for hairlessness:

• h = French hairless cat, recessive.

• hd = British hairless cat, recessive.

• Hp = Russian Donskoy and Peterbald, dominant.

• hr = Canadian Sphynx cat, recessive.
Some rex cats are prone to temporary hairlessness, known as baldness, during moulting.

Here are a few other genes resulting in unusual fur:

The Wh gene (dominant, possibly incomplete) results in Wirehair cats. They have bent or crooked hair producing springy, crinkled fur.
A hypothetical Yuc gene, or York Chocolate undercoat gene, results in cats with no undercoat. However, the proportional relationship between guard, awn, and down hair production varies greatly between all breeds.

A recessive autosomal gene for Onion hair which causes roughness and swelling on the hairs. The swelling is due to enlargement of the inner core of medulla cells.

A recessive autosomal gene spf for sparse fur. As well as sparse coat, the hairs are thin, straggly and contorted and there is brown exudate around the eyes and nose and on the chest and stomach. A similar condition is linked to Ornithine Transcarbamylase Deficiency in mice.