Final answer:
Calico cat coat color arises from X-activation, a sex-linked inheritance where females exhibit varying coat colors due to random inactivation of one X chromosome in different cells, resulting in a unique pattern.
Step-by-step explanation:
The coat color of calico cats is a result of X-activation, which is a form of sex-linked inheritance. In calico and tortoiseshell cats, females heterozygous for an X-linked coat color gene express different coat colors over different regions of their body, correlating with which X chromosome is inactivated in a given region during embryonic development.
This phenomenon occurs because females have two X chromosomes, whereas males only have one, making the tortoiseshell pattern unique to females. When considering patterns of inheritance in cats, codominance is observed since both black and yellow colors are expressed simultaneously in the calico pattern.