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March 15th, 2009, 05:50 PM
Tortoishell Cats

Tortoiseshell describes a coat coloring found in cats. Cats of this color are mottled, with patches of red and black, chocolate, or cinnamon. They are sometimes called torties for short.

The term "tortoiseshell" (also called calimanco or clouded tiger in North America) is typically reserved for cats with brindled coats that have relatively few or no white markings. Those that are largely white with red and black patches (rather than a brindled aspect) are described as tortoiseshell-and-white (in the United Kingdom) or calico (in the United States).

Tortoiseshell cats (also called tri-color or tortie) are often confused with calico cats. The confusion is understandable. Calico cats are mostly white with black and bright orange spots. Tortie cats have the same colors, but very little or no white on them at all. The white fur on torties is usually seen on their paws, belly, and chest. Their brown, black, and orange colorings also blend together more than those of calicoes, giving torties a mottled appearance.

Tortoiseshells and calicos are not specific breeds of cat. The tortoiseshell markings appear in many different breeds. This pattern is especially preferred in the Japanese Bobtail breed.

Both calico and tortoiseshell cats are almost always female.

Tortoiseshell cats have coats with patches of red and black, chocolate, cream, or cinnamon. The size of the patches can vary from a fine speckled pattern to large areas of color. Typically, the more white a cat has, the more solid the patches of color. Dilution genes may modify the coloring, lightening the fur to a mix of cream and blue, lilac or fawn. The markings on tortoiseshell cats are usually asymmetrical. Occasionally tabby patterns of eumelanistic and pheomelanistic colors are also seen (these are often then called "torbie" or "caliby"). Tortoiseshell also can be expressed in the point pattern.

Tortoiseshell coats are caused by a combination of specific genetic traits. In female cats, where this trait occurs almost exclusively, it is a result of X-inactivation, in which different patches of fur receive coding for different hair color due to the activation of an X chromosome from either the mother or the father. Calico coloring is a mix of phaeomelanin based colors (red) and eumelanin based colors (black, chocolate and cinnamon).

Coat coloration in cats is complex, and controlled by several genes. One gene involved has two alleles: the Orange allele, O, which is the dominant form, (XO), and produces orange fur; and the "Black" allele, "o", which is the recessive form, (Xo), and produces black fur.

For a cat to be a tortoiseshell or calico, it must simultaneously express both of the alleles, O and o, which are two versions of the same gene, located at the same locus on the X chromosome. Males normally cannot do this: they can have only one allele, as they have only one X chromosome; consequently, virtually all tortoiseshell or calico cats are females. Occasionally a male calico is born (the rate is approximately 1 in 3,000). These may have Klinefelter's syndrome, the carrying of an extra X chromosome, and will almost always be sterile. Alternatively, a male calico/tortoiseshell may be a chimera, resulting from the fusion of two differently colored embryos.

The spotting gene causes white patches to cover the colored fur. Although there is no genetic difference, the amount of white is artificially divided into mitted, bicolor, harlequin, and van, going from almost no white to almost completely white.

In normal female tortoiseshell cats and in Klinefelter males, the position of the patches depends on which X-chromosome is active in each cell and which is inactivated to become a Barr body.

In some cats, mainly calico cats with a prominently white coat, the texture of hair may change between colors.

Cats of this coloration are believed to bring good luck in the folklore of many cultures in the United States these are sometimes referred to as money cats.