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These are the ones that make them male or female and they play an essential role in determining their colour.
Since males have only one X, they either are or aren't ginger. As far as the cells are concerned two X's is one too many, so each cell deactivates one of the X chromosomes in a fairly random fashion.BIRDS AND THE BEESIt has been my observation that in the cat world tortoiseshell (known in the US as "calico") cats are always female, while all ginger cats are male. As a cat lover myself I always considered the above assertion to be true.That is until one day, when I visited a cat protection league re-homing centre, and saw a female ginger cat suckling her litter of three (all ginger) kittens.In order to explain this we need to consider Kitty genetics.All cats have 19 pairs of chromosomes, and like humans, cats have one pair of sex chromosomes.Sometimes the ginger X will be left on producing a bit of orange fur and in some cells the ginger X will be turned off and the genes for black, brown or other colour fur will be produced. Since males only need to have the orange gene on one chromosome to become ginger, and females have to have it on two, ginger males outnumber females 3 to 1.
To show both orange and another colour such as black or brown a cat has to have two different X chromosomes per cell.Therefore tortoiseshell female cats outnumber males by at least 200 to 1, although I suspect actual figures are much higher.When a male tortie does appear, (a result of a mutation producing two X¿s and one Y) he is invariable sterile and may even exhibit feminine behaviour such as nurturing nearby young.So the answer to your question is that your observation is, as a rule of thumb, spot on as far as tortoiseshell's are concerned, although female gingers are fairly common.All tortoiseshell and tortoiseshell and white (Calico) cats are female. The reason is that in cats the colour gene is carried on the X chromosome.As females have two Xs they can express two colours in the coat, and if black is inherited from one parent and ginger (red) from the other, the result is a calico cat.