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Tortoiseshell cat

The term tortoiseshell cat refers to a coloration pattern caused by a specific genetic trait. It is not a specific breed of cat. The tortoiseshell markings appear in many different breeds.

The coats of tortoiseshell cats are a mixture of colours. Their coats combine black, white, red or ginger, and occasionally silver or ginger tabby patterns. The size of the patches can vary from a fine speckled pattern to large areas of colour. Cats with a basic white colour and red and black patches are known as tortoiseshell-and-white or, in the United States, calico cats.

The tortoiseshell coloration is a sex-linked trait, but neither orange nor black is dominant; instead, the two colours appear in patches depending on which X-chromosome is active in the cell and which becomes a Barr body. Because of this, over 90% of tortoiseshell cats are females. Occasionally a male is born. These have Klinefelter's syndrome and are almost always sterile.