A sex-linked single-gene disorder is usually transmitted from:

Question

Quizplus · Accepted Answer

Sex-linked single-gene disorders are inherited through the sex chromosomes, X and Y. Since females have two X chromosomes, they can carry the gene mutation on one X chromosome and not express the disorder (since they have a second, normal X chromosome). However, if a mother carries the mutated gene on one of her X chromosomes and passes it down to a son, he will inherit the disorder because males have only one X chromosome (inherited from their mother). In contrast, if a father has the mutated gene on his X chromosome, he will pass it down to his daughter(s) because they will inherit a copy of their father's X chromosome in addition to their mother's. Sons do not inherit the X chromosome from their father, so he cannot pass on a sex-linked disorder to his son. Therefore, in this question, the correct answer is C (mother to son).

A Sex-Linked Single-Gene Disorder Is Usually Transmitted From