Male tortoiseshell cat 'genetically impossible'

Male cats, like human beings, have only one X chromosome in their DNA meaning that they should be unable to inherit different colours.

The cat's new owner owner Karen Horne , 38, said: ''As a vet I can tell you that it is genetically impossible to get a male cat that is tortoiseshell coloured.

''My colleagues and I have 30 years of experience between us and we have never seen anything like this.''

Of eight million pet cats in Britain only a couple a year are born male tortoiseshells.

The eight-week-old kitten was brought into Mrs Horne's veterinary surgery in Harpenden, Herts., with his three tortoiseshell sisters by local charity Cat and Kitten Rescue.

But asMrs Horne set about vaccinating the siblings she discovered to her amazement that one was a boy.

Mrs Horne, from nearby Markyate, immediately adopted Eddie into her family of five cats, four dogs and three children.

She said: ''I feel like the luckiest vet ever just to see a tortie tom cat, and even luckier to have him live with me.

''We've decided to call him Eddie after Eddie Izzard, the comedian, as he is essentially a boy dressed in girls' clothing.

''He a perfect cute little fluffy bundle. When he came in to the surgery, we all wanted to offer him a home."

via Male tortoiseshell cat 'genetically impossible' - Telegraph.

Not impossible. Just rare.  This is from wikipedia:

Male cats, like other mammalian males, have only a single X chromosome (XY) that does not undergo X-inactivation: coat color is determined by which allele is present on the X, and they will be either entirely black or orange. Very rarely (approximately 1 in 3,000^[3]) a male tortoiseshell or calico is born. These animals typically have an extra X chromosome (XXY), a condition known in humans as Klinefelter syndrome, and undergo an inactivation process like that in females. As in humans, these cats are almost always sterile because of the imbalance in sex chromosomes. Some male calico or tortoiseshell cats may be chimeras, which result from the fusion in early development of two embryos with different color genotypes. Others are mosaics, in which the XXY condition arises after conception and the cat is a mixture of cells with different numbers of X chromosomes.