in their coat patterns In genetic terms, calico cats resemble
tortoiseshells in most ways, except that the tortoiseshell has no white spotting (
piebald). One anomaly is that, 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 resembling a salt-and-pepper sprinkling. This reflects the genetic effects on relative speeds of migration of melanocytes and
X-inactivation in the embryo. Serious study of calico cats apparently began in 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. In 1959, Japanese cell biologist
Susumu Ohno determined the Barr bodies were
X chromosomes. There are two different alleles in calico cats, one received from each parent, that can determine their fur coloration: each allele is responsible for either orange or black fur. Typically, each allele received would create a solid coat of black and orange fur, but with calico cats X-inactivation occurs at random, which makes for the very distinct fur coat. Calico cats are almost always female because the
locus of the gene for the orange/non-orange coloring is on the X chromosome. 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. Since the Y chromosome does not have any locus for the orange gene, it is not possible for a normal XY male cat to have both orange and non-orange genes together, which is what typically results in tortoiseshell or calico coloring. All but approximately one in ten 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. Male calico cats with Klinefelter syndrome often have behavioral problems such as being antisocial; this is caused by poor cognition and developmental issues. Cats with this chromosome abnormality tend to have poor muscle development that leads to a high risk of broken bones, and it is common for these cats to have a feminine appearance despite being male. Some other affects the syndrome may cause are urinary tract infections and a high amount of body fat, which leads to heart disease, diabetes, and joint pain. Not all male cats with the syndrome are guaranteed to have all the medical issues listed above. 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. The study of calico cats may have provided significant findings relating to physiological differences between female and male mammals. == Folklore ==