Not all, but most gingers are toms; apparently ginger males outnumber females 3 to 1. The reason for this is the difference between the chromosome pairs in the sexes. In females, both sex chromosomes are X, making females XX, whereas males are XY, the Y making them male. The gene for ginger, which will override all other colours, is located on the X chromosome, so as males have only one X, they either are or aren't ginger. As a female has two X chromosomes, the ginger gene would have to be attached to both chromosomes; because if it's only on one, this gene could be deactivated by a cell in the other chromosome. This deactivation is a normal process carried out in a fairly random fashion. 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, in which case the genes for black, brown or other colour fur will be produced, which will produce a Tortoiseshell cat and female tortoiseshell cats are said to outnumber males by at least 200 to 1, although I think this is a pretty conservative estimate. So, to sum up, if the ginger gene is on the male's X chromosome, he'll be ginger, and if the gene is on both the female's X chromosomes, she'll be ginger. More often, however, the gene only attaches itself to one of the female's X chromosomes and this will be deactivated by the other.