Question

ortoise shell cats that are identical twins are very unlikely to have the same splotchy mixture of yellow and black hairs. What is the genetic explanation for this?

Answer 1

Thsi is because of X chromosome inactivation. X inactivation is m important mechanism that leads to dosage compensation in different sexes of a species. As females have two X chromosomes and males have one, the inactivation of one of the X chromosome in the females makes the dose of products of genes present on X chromosome equal. Another feature the regarding this process is that in the somatic cells either of the X chromosome can get inactivated. Imagine a trait with two different alleles on X chromosome. Let's say for coat color the animal has two alleles black and orange. Black is present on X1 and orange on X2. During X inactivation some cells will have their X1 inactivated producing the color orange and some have their X2 inactivated producing black colour.

this takes place in twins also which is why they are very unlikely to same splotchy of hair and coat color.