Question

Cat breeders are aware that kittens expressing the X-linked calico coat pattern and tortoiseshell pattern are almost invariably females.

Which one of the following statements supports this conclusion?

Answer 1

Calico and tortoiseshell patterns in cats occur almost exclusively in females because the gene for coat color is X-linked, and the phenomenon of X inactivation during embryonic development in females leads to these patterns, while males with only one X chromosome do not have a second allele to manifest such variegation.

Step-by-step explanation:

The statement supporting the conclusion that calico and tortoiseshell cats are nearly always female is that in cats, the gene for coat color is located on the X chromosome. During the embryonic development of female cats, one of the two X chromosomes is randomly inactivated in each cell, resulting in a tortoiseshell pattern if the cat has two different alleles for coat color. Male cats, having only one X chromosome, cannot exhibit a tortoiseshell coat because there is no second X to produce the contrasting color patterning.