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Tortoiseshell is a cat color that is the result of a cat with two X chromosomes having one sex-linked orange allele and one non-orange allele. As such, in the real world, all tortoiseshells are either female or intersex.

Calico cats are tortoiseshell cats with high white spotting, though the line is blurry. It is generally accepted that "tortoiseshell" refers to cats with less than 50% white spotting, and usually a more "brindled" pattern.