Feline breeders are usually found of genetics. Indeed, a good understanding of this field is required to determine the genetic selection program of the cattery, especially in order to try to predict the color of the coat, which is obviously one of the main genetic concerns. Indeed 9 different genes are involved, the final coat being the result of the combination of their different effects.
Few years ago, while I was lecturing in Eastern Europe, one cat breeder showed me a picture of one of his young male kitten he was really proud of, because of its unique coat. When I looked at the picture something started bugging me in the corner of my head… Just by looking at the picture, I could already say that this cat had a problem… It was a calico male…
From a genetic point of view, a calico individual should be heterozygous for the orange gene O. This means this individual needs to have two different alleles of this gene in its genetic material. Why is it a problem? Because the orange gene is carried by the sex chromosome X… A calico cat imperatively has two X chromosomes… and therefore be a female! A calico male (males are supposed to be XY) will definitely have a genetic abnormality since it must carry two X chromosomes. This abnormality usually impairs spermatogenesis (sometimes the gonads are even a mix of ovarian cells and testicular cells, called ovotestis) and leads to infertility. The same goes for the tortoise-shell males, which are also heterozygous for the O gene and therefore imperatively carry two X chromosomes.
These abnormalities are not that rare in breeding cats. It does not mean that the cat is not healthy (most of them will have a perfectly normal life), but however remember that you will not be able to use them for breeding!
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