Are all calico cats female?

Calico cats are almost always female, although there are rare male calicos. The orange and black genes that create the calico pattern are linked to the X chromosome, so only cats who have two X chromosomes can display both colors.

Normal male cats have two chromosomes, one X and one Y. These cats can have either black or orange fur, but not both. Male calico or tortoiseshell cats have an extra chromosome, giving them two X and one Y. This gives them a male sex while still being able to display both orange and black fur together. Cats with this genetic abnormality are almost always sterile, however.