Why are male calico cats sterile?
Since two X chromosomes in an animal means that it is female and a XY sex chromosome layout means that the animal is male, it is extremely rare for a male cat to have both the orange and the black X chromosomes required for the calico coat. For this to be possible, the male cat must have a XXY layout of chromosomes – the equivalent of the human Klinefelter’s Syndrome. This syndrome almost always leads to the sterility of the animal that has it, although there have supposedly been cases where individuals with Klinefelter’s have been fertile. And as to why Klinefelter’s causes sterility, I don’t have a clue.
