A calico cat has white fur with patches of black and orange. The orange patches may be reddish or reddish brown. Calico cats differ from tortoiseshell cats, which have black and orange patches but little or no white coloring.
Ninety percent of calico cats are female. The few male calico cats are genetic anomalies and are almost always sterile.
A cat's coloring is determined by X chromosomes. Females have two X chromosomes, and a calico cat has one black X chromosome and one orange X chromosome. The white color is associated with a different gene. A male cat normally has a Y chromosome along with one X chromosome that determines its color. A male calico has a Y chromosome and two X chromosomes; the X chromosomes give the male cat the calico coloring.