By Jennifer Copley (Last Updated 9 April 2011)
What Is a Tortoiseshell Cat?
The coats of tortoiseshell cats are made up of mottled orange, cream, or brown and black patches. The coat is actually a mix of two coat types: red (orange) tabby and black. As both these genes are sex-linked (carried on the X chromosome), only a cat with two X chromosomes can inherit the combination. Males normally have one X and one Y.
Why Are There a Few Male Tortoiseshell Cats?
From time to time a genetic error causes a male cat to have an extra X chromosome, manifesting an XXY pattern. This enables the cat to develop a tortoiseshell coat but still have masculine characteristics as a result of the Y chromosome.
Because they are so rare, tortoiseshell tom cats became the subject of a number of superstitions. The Celts felt it was a good omen to have a tortoiseshell tom settle in their homes, and the English believed that rubbing a wart on the tail of a male tortoiseshell cat would remove it, though only if done during May. Japanese fishermen also sought out male tortoiseshell cats to keep on their ships for protection against storms and ancestral ghosts.
Are Tortoiseshell Toms Different from Regular Tom Cats?
Male tortoiseshell cats are sterile and their behaviour is more like that of masculinized females than ordinary males. Observations of one male tortoiseshell revealed that he ignored both the status battles among males and those among females in the cat colony where he resided. He also allowed mating attempts from young males but did not seek out females in heat until he was older.
Are Calico Cats Always Female?
Calico cats are tortoiseshell cats with white patches. The calico pattern also requires two X chromosomes – one for the red fur gene and one for the black fur gene. Therefore, most calicos are female, and male calico cats have the rare XXY chromosome pattern.
For more cat articles, see the main Cats page.
Reference: Morris, D. (1987). Catlore. London: Jonathan Cape Ltd.