Practice question

X-linked recessive carrier females are heterozygous X^A X^a possessing one normal and one mutant allele. One normal allele typically produces sufficient functional protein for normal physiology, and random X-chromosome inactivation creates mosaic tissue where roughly half cells express normal allele, preserving normal phenotype clinically. They remain healthy but carry fifty percent risk of transmitting mutant allele to sons who become affected and to daughters who become carriers themselves. Phenotypically normal carrier status explains why trait appears to skip generations through maternal line before reappearing in male relatives.