Essential Genetics 6th Edition by Daniel Hartl

Exercise 11

A recessive mutation in the human genome results in a condition called anhidrotic ectodermal dysplasia, which is associated with an absence of sweat glands. The condition can be detected by studies of the electrical conductivity of the skin, because skin without sweat glands has a lower electrical conductivity (higher resistance) than normal skin. In kinships in which the recessive allele is segregating, affected males are found to show low conductance uniformly across their skin surface, as do affected females. However, many females show a mosaic pattern with normal conductance in some patches of skin and low conductance in others. The pattern of tissue lacking
Sweat glands is different for each mosaic female examined. How could this pattern of gene expression be explained?