Selective breeding has reduced the tabby markings to produce a cat that looks solid red by breeding from those cats with the least red markings (cats with 'low contrast' between markings and background colour). A variety of other genes, called polygenes or modifiers, control the intensity of colour and contrast between markings and background colour. If it occurs later, the patches are smaller as the cells have less room to multiply into some 'patches' will be no larger than a single hair! All 'red' cats are red tabbies - where there are large red patches, the tabby pattern will usually be discernible.Īll Red Cats Are Red Tabbies? Strange as it may seem, all red cats are actually red tabby because the non-agouti gene (the gene that turns a tabby into a self/solid colour) does not affect the way red pigment is deposited. If deactivation occurs early on each pigment cell has room to multiply into, a 'red' cell will multiply into more red cells while a 'black' cell will give rise to patches of black. Skin cells multiply during growth and spread out across the skin as the embryo grows the skin cells multiply. One (the 'early/late deactivation theory') suggests that the time at which X chromosome deactivation occurs during foetal growth determines whether the cat has well defined patches or is brindled with intermixed black and orange hairs. There are two main theories regarding brindled torties and patched torties. Male cats only inherit one X chromosome so this is active in all skin cells as there is nothing equivalent on the Y chromosome which could 'switch off' the O gene.

This can only happen in cats with two X chromosomes. The skin is a mosaic of cells where some have the O gene active (making ginger pigment) and some do not (making black pigment). This occurs early on in the embryo and as skin cells multiply, they form patches. This only shows up visibly in skin cells as these produce pigment. Some cells randomly activate the O gene while others activate the gene in the equivalent place on the other X chromosome. The formation of red and black patches in a female with only one O gene is through a process known as X-chromosome inactivation. Tortoiseshell cats are therefore heterozygous (not true-breeding) for red colour. The O gene is called a sex-linked gene because it is carried on a sex chromosome. If she inherits only one O gene, she will be tortoiseshell.

She must inherit two O genes to be a ginger cat.

A normal male cat has XY genetic makeup he only needs to inherit one O gene for him to be a ginger cat. The O gene is carried on the X chromosome. The O gene changes black pigment into a reddish pigment.

The ginger colour of cats (known as 'yellow', 'orange' or 'red' to cat breeders) is caused by the 'O' gene. Jean Bungartz referred to tortoiseshell-and-white cats as 'Spanish cats' in his 1896 book 'Die Hauskatze, ihre Rassen und Varietäten' (Housecats, Their Races and Varieties) in ' Illustriertes Katzenbuch' (An Illustrated Book of Cats) though he said it was hard to explain why they got the name as they were not restricted to the Pyrenean peninsula. This article only considers normal tortoiseshell cats. These are discussed in detail in ' Mosaicism, Tortie Tomcats, Genetically Impossible Kittens and Gender Anomalies'. The very few male tortoiseshell cats are caused by genetic aberration or development abnormalities in the foetus. Because of the way tortoiseshell is inherited, almost all tortoiseshell and calico cats are female.

Calico tortoiseshell cats always female