So in many cases, there's no conflict, at least about orange coloration - the two cell lines agree. And if both X's said, "nope, no orange fur on this kitten!" she won’t have any orange hair. If both maternal and paternal X's said "this kitten will have orange in her coat," she will. What does this have to do with calicos? Remember, "O" is carried on X. So henceforth, the developing kitten will be composed of cells descended from two different cell lines: the ones in which the maternal X was inactivated, and the ones in which the paternal X was turned off. In concept, the process is marvelously simple: One X chromosome in each of the developing embryo's cells is "turned off." (At that point, that X chromosome is "compressed" into a mere shadow of its former self and is thereafter called a Barr body.) X-inactivation is random, irreversible, and is passed down to all the cell's descendents. This process is called random X-inactivation. The female's two X's obviously carry some redundant genetic information, so nature has devised a clever and splendidly efficient way of sorting out which genes will determine the kitten's phenotype, or physical makeup. Interestingly, while "O" is the only sex-linked color-coat gene in cats, in animals other than cats that can display "calico" coats, the relevant genes are not sex-linked! "O" specifies either orange fur or not-orange (i.e., black) fur. The gene for orange coat color (called "O") is carried only on the X chromosome, so it's called a sex-linked gene. Therefore, the X pulls a lot more weight in determining certain physical traits. The Y chromosome, the one that determines maleness, is much shorter, and carries less genetic information, than the X. A normal female cat has two X's ("XX") a normal male cat has one X and one Y ("XY"). When a male cat's sperm fertilizes a female's egg, It bequeaths either an X or Y to the embryonic kitten, determining its gender. Normally, each kitten gets an X from Momcat and either an X or Y from Dad. But there's no single "calico gene." Calico and tortoiseshell cats result from a complex chain of interactions very early in a kitten's development.Įach of a cat's 38 chromosomes is part of a nicely-matched pair -except those dubbed "X" and "Y," the sex chromosomes. Bell, Clinical Assistant Professor of Genetics at Tufts University School of Veterinary Medicine in North Grafton, MA. They brag about sparkling personalities and striking looks, often attributing both to what some call the "fire gene." "Most veterinarians will attest that in general, calicos and torties have a more 'mercurial' or 'intense' personality," agrees Jerold S.
One thing's certain - owners of calicos know their cats are special. How had the apparently common belief that tri-colored cats were worth big bucks gotten started? Was it an urban myth? Or was there more to it? And what makes a calico, a calico, anyway? My neighbor was predictably vague about just who might be willing to write me that big check. "You could sell her, for a lot!" Petunia was worth the world to me, but I'd never heard of anybody cashing in on a shelter kitten. "Oh, you have a money cat!" exclaimed my neighbor upon meeting my calico, Petunia.
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