Calico cat

The coat pattern of calico cats does not define any breed, but occurs incidentally in cats that express a range of color patterns; accordingly the effect has no definitive historical background. However, the existence of patches in calico cats was traced to a certain degree by Neil Todd in a study determining the migration of domesticated cats along trade routes in Europe and Northern Africa.[5] The proportion of cats having the orange mutant gene found in calicoes was traced to the port cities along the Mediterranean in Greece, France, Spain and Italy, originating from Egypt.[6] The calico has been Maryland's state cat since October 1, 2001. Calico cats were chosen as the state cat because their white, black, and orange coloring resembles the coloring of the Baltimore oriole (the state bird) and the Baltimore checkerspot butterfly (the state insect).

In genetic terms, calico cats are tortoiseshells in every way, except that in addition they express a white spotting gene. There is however one anomaly: as a rule of thumb the larger the areas of white, the fewer and larger the patches of ginger and dark or tabby coat. In contrast a non-white-spotted tortoiseshell usually has small patches of color or even something like a salt-and-pepper sprinkling. This reflects the genetic effects on relative speeds of migration of melanocytes and X-inactivation in the embryo.[7]

Serious study of calico cats seems to have begun about 1948 when Murray Barr and his graduate student E.G. Bertram noticed dark, drumstick-shaped masses inside the nuclei of nerve cells of female cats, but not in male cats. These dark masses became known as Barr bodies.[8] In 1959, Japanese cell biologist Susumu Ohno determined the Barr bodies were X chromosomes.[8] In 1961, Mary Lyon proposed the concept of X-inactivation: one of the two X chromosomes inside a female mammal shuts off.[8] She observed this in the coat color patterns in mice.[9]

Calico cats are almost always female because the locus of the gene for the orange/non-orange coloring is on the X chromosome.[10] In the absence of other influences, such as color inhibition that causes white fur, the alleles present in those orange loci determine whether the fur is orange or not. Female cats, like all female placental mammals, normally have two X chromosomes. In contrast, male placental mammals, including chromosomally stable male cats, have one X and one Y chromosome.[2][8][11] Since the Y chromosome does not have any locus for the orange gene, there is no chance that an XY male could have both orange and non-orange genes together, which is what it takes to create tortoiseshell or calico coloring.

One exception is that in rare cases faulty cell division may leave an extra X chromosome in one of the gametes that produced the male cat. That extra X then is reproduced in each of his cells, a condition referred to as XXY, or Klinefelter syndrome. Such a combination of chromosomes could produce tortoiseshell or calico markings in the male, in the same way as XX chromosomes produce them in the female.[12]

All but about one in three thousand of the rare calico or tortoiseshell male cats are sterile because of the chromosome abnormality, and breeders reject any exceptions for stud purposes because they generally are of poor physical quality and fertility. Even in the rare cases where a male calico is healthy and fertile, most cat registries will not accept them as show animals.[13]

As Sue Hubble stated in her book Shrinking the Cat: Genetic Engineering Before We Knew About Genes,

The mutation that gives male cats a ginger-colored coat and females ginger, tortoiseshell, or calico coats produced a particularly telling map. The orange mutant gene is found only on the X, or female, chromosome. As with humans, female cats have paired sex chromosomes, XX, and male cats have XY sex chromosomes. The female cat, therefore, can have the orange mutant gene on one X chromosome and the gene for a black coat on the other. The piebald gene is on a different chromosome. If expressed, this gene codes for white, or no color, and is dominant over the alleles that code for a certain color (i.e. orange or black), making the white spots on calico cats. If that is the case, those several genes will be expressed in a blotchy coat of the tortoiseshell or calico kind. But the male, with his single X chromosome, has only one of that particular coat-color gene: he can be not-ginger or he can be ginger (although some modifier genes can add a bit of white here and there), but unless he has a chromosomal abnormality he cannot be a calico cat.[6]

It is currently very difficult to reproduce the fur patterns of calico cats by cloning. Penelope Tsernoglou wrote "This is due to an effect called x-linked inactivation which involves the random inactivation of one of the X chromosomes. Since all female mammals have two X chromosomes, one might wonder if this phenomenon could have a more widespread impact on cloning in the future."[14]

Calico cats may have already provided findings relating to physiological differences between male and female mammals.[8][11][15]

Cats of this coloration are believed to bring good luck in the folklore of many cultures.[16] In Germany, the word for a cat with calico coloring is "Glückskatze"; literally, "lucky cat." In the United States, these are sometimes referred to as money cats.[17] A cat of the calico coloration is also the state cat of Maryland in the United States.[18] In the late nineteenth century, Eugene Field published "The Duel", a poem for children also known as "The Gingham Dog and the Calico Cat". In Japan, the Maneki-neko figures depict calico cats, bringing good luck; Japanese sailors often had a calico ship's cat to protect against misfortune at sea.[19]

• Bicolor cat
• Brindle
• Cat coat genetics
• Deaf white cat
• Maltese cat
• Point coloration
• Tabby cat
• Tortoiseshell cat

• Media related to Calico cats at Wikimedia Commons