Male calico cats typically have a chromosomal aberration of two X chromosomes and one Y chromosome (XXY). Cats with this chromosomal configuration are usually sterile (not able to breed). This is similar to a condition in humans called .
A single can have either a black (version) of the coloration or an orange version, but not both. However, a female cat has two X chromosomes, so it can have both versions, black on one chromosome and orange on the other, making the cat a calico. A male cat usually has one X chromosome and one Y chromosome. A does not have a color gene, so the cat can have either an orange or a black gene, but not both. Calico cats are often used as an example in classes when discussing .
Calico cats have sections of different colors in their fur. Usually, the calicoes that have more white fur also have larger and more distinct patches of color. If the orange and black fur is mixed, the cat is called a . , or "torties," as they are commonly known, have little or no white fur.
These cats were chimeras - that is when their mother was pregnant with them two fetuses merged in the very early developmental stages. This created a perfect cat with two types of DNA. One set of DNA gave the cat its calico color while another set gave it its reproductive parts. In essence the cat may have been calico but his sex was not.