A quick Wiki lookup explains that: "Because genetic determination of some coat colors in cats is linked to the X chromosome, calicoes are nearly always female. Because of the genetics involved, calico males generally have impaired vitality and are almost always sterile."
Not being very knowledgeable about feline genetics, I never would have guessed that.
For those not in the know it should be further explained that Calico cats aren't a specific race of cats, but referes to cat with a spotted or striped coat.
