Calico cats are almost always female. That said, exceptions to this rule can occur with atypical genetics due to mutations or chimeras, resulting in the elusive male calico cat. The calico coat involves a combination of orange, black and white patches. The genetics behind a cat’s coat coloration are complicated, with genetics playing a role in the color, dilution of color and any markings present to give your furry friend their unique appearance.
Cat Genetics 101
Cats have 19 pairs of chromosomes, with each set containing numerous different genes. As with people, all cats receive one X chromosome from their mother, and either one Y or one X chromosome from their father. Females carry two X chromosomes and males carry both an X and a Y chromosome. Cats receiving two sets of X chromosomes (XX karyotype) are female and cats receiving one set of each X and Y chromosomes (XY karyotype) are male. Genes then each have two alleles, which can be either both dominant (e.g. OO), both recessive (e.g. oo) or heterozygous with one of each (e.g. Oo). If a dominant allele is present, this is the trait that is physically displayed in a cat’s phenotype, whereas if both alleles are recessive, this trait is displayed.
Orange Versus Black Coloration
Why are genes so important, you might ask? The location on the gene that expresses color can express either orange or black. The tricky part is that the orange coat color alleles are only found on the X chromosome, making this a sex-linked trait. As a result, male cats only have one copy of this allele. If they receive a dominant orange (O) allele from their mother, the location that expresses black is blocked, so they will be orange. Whereas a recessive allele (o) is non-orange, allowing the black coat color to be present. Female cats, however, have two X chromosomes, allowing them to express either an entirely orange coat (OO), entirely black coat (oo) or patches of both black and orange (Oo). The black and orange coat combination is known as a tortoiseshell cat. Contrary to popular belief, all orange cats are not male and are just as likely to be female.
Why Do Cats Have White Spots?
White spots, sometimes referred to as piebald spotting, are expressed on both the X and Y chromosomes, so this is not a sex-linked trait and can be expressed equally in cats of both genders and with any color coat. In order to achieve the full calico appearance, cats that are tortoiseshell with the heterozygous orange gene (Oo) must also develop white patches. Cats with a recessive (ss) spotting gene do not display any white patches, but those that have dominant spotting alleles in their genetic makeup (SS or Ss) will have white patches.
Male Calico Cats – They Exist!
With a typical genetic situation, calico cats are females with an Oo/SS or Oo/Ss genotype. Male cats have calico or tortoiseshell coats if they have an extra X chromosome or are a chimera. In cats with a condition called Klinefelter’s syndrome, males have an extra X chromosome, resulting in an XXY chromosomal makeup rather than the typical XY. Chimeras occur when two embryos are fused together during development, resulting in the combination of genetic material, yet this is very rare. The only way to differentiate between the underlying genetic explanation for a male calico cat is through genetic testing. It is important to note that while male calico cats exist, they are nearly always sterile.
The genetics behind a cat’s coat colors are far more complex than described here. For example, the tabby cat has a variety of different alleles that can result in different striped, patchy or ticked patterns. Cats may have an agouti gene, which can result in variations in the color on a single strand of hair. Genetics also play a role in the specific shade of a coat color by affecting the distribution of melanin (pigment) within the hair.