Males with a recessive X-linked recessive allele that causes a disorder don't always show symptoms because they can also carry a dominant allele on their Y chromosome.

Question

Quizplus · Accepted Answer

Males only have one X chromosome and one Y chromosome, and the Y chromosome does not carry the same genes or alleles as the X chromosome. Therefore, a dominant allele on the Y chromosome cannot mask the effects of a recessive X-linked disorder allele. If a male inherits a recessive X-linked disorder allele on his X chromosome, he will have the disorder because he does not have another X chromosome with a dominant allele to override it.

Males with a Recessive X-Linked Recessive Allele That Causes a Disorder