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Close your eyes and imagine the proverbial kitty sprawled out on a rug in front of a blazing fireplace. What kind of cat does your imagination conjure up? For many people, it would be a calico, a lovely little female with a patchwork of orange, white and black fur. The image of the calico cat is so pervasive, it is referred to in poetry, graces the covers of many a cat magazine, appears on numerous boxes of cat food and hangs in museums around the world. I recently received an interesting e-mail that read, "I had heard that most, if not all, calico cats are female. I find this difficult to believe. Is it true? " As difficult as it might be to believe, it is true. In order to understand why, here's a quick lesson in genetics: The genes that control feline coat color are found on the X chromosome. Females have two X chromosomes; males have an X and a much smaller Y. (During fertilization, the female contributes an X to the embryo, whereas the male contributes either an X or Y. If it is an X chromosome, the embryo is female; if it's the Y, the result is a male kitten.) To compensate for this imbalance, part of one of the female's X chromosomes, on which the genes for orange, black and white coat color are coded, is inactivated or turned off. Inactivation takes place several days after fertilization when the embryo has grown from a single cell to a cluster of cells. It is a random act as to which X chromosome is inactivated in each cell. In some cases, it might be the gene for white coat color; in other cases, it will be black. This random turning off of genes results in the unique patterning of the calico and tortoiseshell cat. It is a rare genetic occurrence, but a male calico can result. This cat will have two X chromosomes and a Y chromosome, and will usually be sterile.
This original handpainted Calico Cat Wall Clock is just one of the pieces available from Cat Crazy. |
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