• CFA defines the calico cat as a female cat with white and large solid areas of black and red, blue and cream, or lilac and cream.
  • CFA states that calico, like tabby and tortoiseshell, refers to the cat's pattern and not to its breed.
  • The 2025 Current Biology paper on sex linked orange describes calico color patches as expanded relative to a tortoiseshell's, caused by an autosomal dominant white spotting mutation at the KIT locus.
  • Orange itself is a 5 kb deletion at the X linked ARHGAP36 gene, and the calico coat is a visible readout of random X inactivation, the process Mary Lyon proposed in 1961.
  • Male calicos occur but are unusual; the closely related tortoiseshell male examined in 2014 carried a 39,XXY karyotype and showed complete loss of germ cells.

What to look at

  1. Confirm three elements are present: white, a red or cream, and a black, blue or lilac. Two colors without white is a tortoiseshell rather than a calico.
  2. Check that the color sits in large solid blocks with clean boundaries, which is what the white spotting gene produces, rather than intermingled through the coat.
  3. Read the dark color. Black with red is the standard calico; gray with cream is a dilute calico, and CFA lists blue and cream as one of the pattern's color combinations.
  4. Look inside the dark blocks in sunlight. Tabby stripes inside the color make the cat a patched tabby and white rather than a plain calico.
  5. Check the registry category. CFA files calico under parti-color patterns, so white plus large solid color blocks should carry the identification.
  6. Assume female unless there is reason not to, because the pattern needs two X chromosomes, and treat a calico tom as a case for a veterinary chromosome test rather than a guess.

Two genes make a calico

A calico is a tortoiseshell plus white, and each half has its own gene. Sex linked orange is a 5 kb deletion at the X linked ARHGAP36 locus, identified in 2025, and in a female carrying it on only one X chromosome, random X inactivation produces a mosaic of orange and nonorange clones. That is the tortoiseshell. The white is separate and autosomal: a dominant white spotting allele at the KIT locus, which in the 2014 G3 study was traced to a full length feline endogenous retrovirus inserted into a conserved regulatory site in KIT intron 1. The white does not just add a third color. It reorganizes the mosaic, pushing the orange and black into the larger solid blocks that make a calico recognizable.

A textbook that walks around the house

Calico cats are not merely an example of X inactivation. They are part of how the idea was established. The 2025 Current Biology paper states that the patchwork coloration of calico and tortoiseshell cats played a central role in conceptualizing X chromosome inactivation and fed into Mary Lyon's original 1961 theory. The mechanism is visible because each patch is a clone: one X is silenced early in development and its descendants inherit that choice, so a patch of skin expresses only one allele. The same paper notes that sex linked orange has no counterpart in most mammals, being known only in the domestic cat and the Syrian hamster, and offers that as the likely explanation for the absence of calico dogs and calico mice.

What a photo can and cannot tell you

A photo is reliable here. Whether white is present, how large and how clean edged the color blocks are, whether the dark is black or gray, and whether tabby stripes run inside the color are all surface features that a daylight full body shot resolves. What a photo cannot do is name a breed, because calico is not one and CFA says so directly. A calico coat can sit on a Persian, a Maine Coon or an unregistered domestic shorthair, and the pattern itself carries no breed information. The photo also cannot confirm sex or karyotype, so an apparent calico tom is a question for a veterinarian, not for an image.

Related guides

Sources