• CFA defines a bicolor as a parti-color cat with solid areas of white and another color or pattern, and lists black and white among the usual bicolor colors.
  • CFA states that all the colors occurring in the bicolor cat can occur in male and female cats, so a tuxedo pattern carries no sex bias.
  • The white comes from the W locus on chromosome B1, identified as KIT, where a full length feline endogenous retrovirus insertion is associated with white spotting and a solitary long terminal repeat with dominant white.
  • That same 2014 G3 study linked the marker to deafness, with dominant white and blue iris showing complete penetrance for coat but incomplete penetrance for deafness and iris hypopigmentation.
  • CFA calls a bicolor with more white than color a bicolor van, in which most of the color sits on the ears and the tail.

What to look at

  1. Confirm the two colors. Solid black and solid white, in separate areas rather than mixed, is the pattern. Red and white, cream and white, and blue and white are the other usual bicolors CFA lists.
  2. Read the amount of white. A bib, white paws and a belly stripe is the classic tuxedo distribution. Once white covers more of the cat than color, CFA calls the result a bicolor van, with the color concentrated on ears and tail.
  3. Check the black in sunlight. Ghost tabby stripes showing through the dark areas mean the cat is a black and white tabby rather than a solid black and white.
  4. Check for any red or cream. Even a small patch of red or cream, or mottled black and cream paw pads, moves the cat out of bicolor and into the tortoiseshell and white group.
  5. Check the eyes. Eye color in a bicolor is not fixed by the pattern, and CFA notes that white or predominantly white cats may have blue eyes, gold or copper eyes, or one of each.
  6. Check both sexes are plausible. Unlike calico and tortoiseshell, a tuxedo pattern gives no information at all about whether the cat is male or female.

What makes the white

The white is an insertion, not a pigment. Linkage work published in G3 in 2014 identified KIT on chromosome B1 as the feline W locus and traced two distinct phenotypes to the retrotransposition of a feline endogenous retrovirus into the gene. A full length 7,125 base pair element is associated with white spotting, the pattern that produces a bib, white paws and a tuxedo. A long terminal repeat alone is associated with dominant white, the fully white cat. The insertion interrupts a regulatory site in KIT intron 1 that is conserved across mammals and controls where and when KIT is expressed in melanocytic cells, which is why the white lands in patches rather than evenly.

Why tuxedos are not sex biased

This is the cleanest contrast with calico and tortoiseshell. Those patterns depend on a gene on the X chromosome, which is why a cat needs two X chromosomes to wear both colors at once and why CFA writes both definitions in the female. White spotting sits on an autosome, chromosome B1, and is inherited independently of sex. CFA states the consequence directly: all the colors that occur in the bicolor cat can occur in male and female cats. So a tuxedo tells you nothing about the cat's sex, and the common assumption that black and white cats are usually male has no genetic basis of the kind that makes calicos female.

What a photo can and cannot tell you

A photo handles this pattern easily. Whether the cat is black and white rather than tortoiseshell and white, how much of the coat is white, where the white falls, whether ghost tabby shows in the dark areas and what color the eyes are all read directly off a daylight image. What a photo cannot do is make the pattern into a breed, because tuxedo is not one. Black and white bicolors turn up in pedigreed Maine Coons, British Shorthairs and Persians, and in very large numbers of unregistered cats. The photo also cannot assess hearing, which the KIT work associates with dominant white rather than with white spotting.

Related guides

Sources