Friday, March 16, 2012

In Search of White

Harrison Weir's purpose in starting cat shows was to promote the welfare of all cats, not just special breeds. Many cat blogs promote and sell a particular breed of cat. This blog promotes cats who are found in shelters. Sometimes shelter cats are purebreds, and as I find them, I will post them here. But I love mixed breeds, who combine the traits of several different cats.  I write about purebreds, too, and I have no intention to disparage them, any more than a Siamese cat site intentionally disparages Persian cats. But I love the mixed breed; this is what I am "selling" on this particular post.

Daisy is a sweet, friendly 5-year-old white cat with blue eyes who is up for adoption. Her owners had to leave her when they moved. She is used to other cats. She is spayed; she has all her claws.

Daisy is hard of hearing, not totally deaf. Hearing problems are common with many beautiful blue-eyed white cats. Her fur is soft, like a chinchilla rabbit.

 If you are interested in finding out more about her, contact Deer Ridge Animal Hospital in Jackson, MO, at (573) 243-3200.

If you don't live around Jackson, MO, contact a shelter near you. I'm sure there are lots of other beautiful white cats waiting for a home!

Why are white cats often deaf?

Somewhere between 65 and 85 percent of solid white cats with blue eyes have congenital deafness. It is caused by the Dominant White gene, which suppresses the production of melatonin and thus all color in the cat's fur and skin. Every cat has a gene for the expression of color, but in the white cat, that gene is "turned off." It may affect the cat's eyes, creating the blue eyes, and also may prevent the inner ear from forming correctly, thus creating a deaf cat. Cats that are white but only have one blue eye and one eye of another color are often only deaf in the ear that is on the same side of the head as the blue eye.

Because White is dominant, if a cat has only one W gene and one w gene, carrying color, it will always be white. Whether the cat is WW or Ww, breeders still have not developed a fool-proof way of breeding white cats that are never deaf.

Persians, Turkish Angoras, and Turkish Vans are long-haired cats that can be pure white. In the shorthair variety, there is the domestic shorthair, and the White Oriental--a cat that looks like a Siamese but without the points.

 Jubilee lost her whiteness as she got older, like all Siamese--
a great disappointment to 19th century breeders who were
 in search of "white" from the albino cat.
 The Albino Gene

Siamese cats, which are born white, get their white color from a different gene--the albino gene. This gene has a spectrum of expressions, ranging from full color to full-blown albinism, in which the animal has totally white hair and skin, and pink eyes. In between these extremes are the burmese allele, which results in muted color; the temperature-sensitive albinism allele, which creates the Siamese cat; and the blue-eyed albino.

This gene is not related to deafness. However, as with albinism in all species, there can be vision problems. Albinism inhibits the normal development of the visual cortex, so that the animal does not develop stereoscopic vision. This is often the cause of crossed eyes in the Siamese. Still, it does not present a serious vision problem to most cats.

The Siamese cat is born white, but does not stay all white, especially when taken out of the tropical climate from where it was bred. For centuries, breeders have sought to develop a white cat that did not have the threat of deafness in its genes and maintained its beautiful white coat throughout its life. The albino gene was not the answer.

And then they were one!

In the 1962, breeder and cat geneticist Pat Turner began mating Seal Point Siamese with White Domestic Shorthair cats. Her goal was to create a white Siamese with blue eyes, but without the genetic trait that can create deafness in cats.  The Foreign white is basically a white Siamese with blue eyes. Introducing the Dominant White gene into the breed again risks deafness, although the breed is carefully monitored.

All white cats, whether or not their hearing or vision is impaired, have a greater risk of skin cancer.

Humans love white cats, but nature doesn't. So why did nature provide for the possibility?

The White Spotting Gene

There is another gene in the cat genome that creates white by masking color: the white spotting gene. It is responsible for the white locket, the white mitted feet, and the various white markings on any part of a cat's body. Occasionally,  this gene creates a cat that is essentially all white.

Tiger's white chin and feet help her blend
into the natural environment.
The S gene works exactly the same as the W gene, and if by chance it should touch the cat's ears, it makes the animal deaf in the same way. But most of the time it doesn't. It just adds interest to the cat's looks. Humans select for the prettiest arrangement of white--the feet, the face, and the underbelly. Less attractive arrangements are largely phased out by human selection. But nature likes the white spots for a different reason--they have a camouflage advantage. In the forests where the European wildcat originated, white spots mimic beams of light streaming through the trees.

The W gene may have been a mutation of S that nature made by mistake, which humans loved so much that they kept it going.

And what of the albino gene?

As already mentioned, the albino gene comes in a spectrum of effects. Complete albinos are at a serious disadvantage, but what about muted colors? Gray instead of black? Tan instead of brown? Pretty, but also a pretty good camouflage if the cat lives on the sandy shore of the Mekong River, where the Siamese breed originated. The burmese allele is commonly found in the street cats of Thailand. One step beyond that is the Siamese allele, and that is not so bad, either.

Vanilla and chocolate varieties of the street cats in Laos


This Siamese kitty blends in with the light sandy soil.


Blue eyes are beautiful, too!

Blue eyes are found randomly in cats that are not all white. Usually, they have some white, thanks to the old White Spotting gene.There is another relatively new breed claimed to have blue eyes NOT linked to coat color. The Ojos Azules (Spanish for blue eyes) breed may be found in any color, but white patching on the peripheral parts of the cat, particularly the tips of the feet and tail, are a common manifestation of the Ojos gene. Less white is considered most desirable, except in colorpoint, where the typical white peripheral tipping is necessary to illustrate that this is a true Ojos Azules and not a colorpoint Oriental.

Ojos Azules have deep blue eyes. Because this supposed gene is not linked to any certain fur color or pattern, it gives the opportunity to have cats with dark coats and blue eyes. It does not cause squinting, deafness, or cross-eye.

But the breed is not without its problems. When the "gene" is homozygous (the cat has the trait from both parents), it causes cranial deformities, white fur, a small curled tail, and stillbirth. However, when the gene is heterozygous (from only one parent), those lethal genetic mutations do not manifest. The result is that breeders must cross the blue-eyed cats with non-blue-eyed cats, assuring a litter of about 50/50 blue/non-blue-eyed kittens. Although only half of the kittens are then part of the Ojos Azules breed, this avoids having much of the litter comprise deformed and /or dead kittens.

This is not a real breed, then, if another breed must be introduced every generation.

I found some experts that even doubt this breed really exists, saying that the pictures might be doctored. In Massimo Picardello's book on feline genetics, no such gene is mentioned.

Fake or not, this cat's blue eyes do seem to present a problem even more serious than that of the other breeds.

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