What do sex-linked genetic diseases involve?

Sex-linked genetic diseases are primarily associated with defects on the sex chromosomes, which are the X and Y chromosomes. These diseases are often caused by mutations or abnormalities on these chromosomes. Most commonly, sex-linked conditions are found on the X chromosome, as it carries a wider array of genes compared to the Y chromosome. Because males have only one X chromosome (paired with a Y), any mutation on that X chromosome will manifest as a disorder, whereas females have two X chromosomes, and the presence of a normal allele on one X can often mask a defect on the other. Thus, the hallmark of sex-linked genetic diseases is indeed the presence of a defect on a chromosome, specifically one of the sex chromosomes.