O locus — orange (red)

Controls: Red/cream colouring, and tortoiseshell in females.

How it works

The orange gene sits on the X chromosome and replaces black pigment with red. Because females have two X chromosomes, a female carrying both red and a black-series colour shows both in patches — a tortoiseshell.

Alleles

ORed (orange)Recessive

oNon-redRecessive

Colours it produces

Red (Ginger)Cream Tortoiseshell

Frequently asked questions

Why are most tortoiseshell cats female?+

Showing red and a black-series colour together normally needs two X chromosomes, so torties are almost always female.

Related genes

B locus — black series

Whether the black pigment shows as black, chocolate or cinnamon.

D locus — dilution

Whether a colour is dense (full) or dilute (softened).

A locus — agouti (tabby vs solid)

Whether the tabby pattern is visible or hidden under a solid coat.

See these colours on real cats.

Browse cat colours