Final answer:
A man with an X-linked harmful allele will pass it to all of his daughters, making them carriers if the allele is recessive, as males have XY sex chromosomes. This results in X-linked disorders being more common in males, who only need one copy of the recessive allele to exhibit the disorder.
Step-by-step explanation:
A man who carries a harmful allele for a sex-linked gene on the X chromosome will pass the allele on to all of his daughters, none of his sons. Since males have XY sex chromosomes, they pass on their Y chromosome to sons and the X chromosome to daughters. In the context of X-linked recessive disorders such as red-green color blindness or hemophilia, this explains why these conditions are more frequently observed in males. To manifest an X-linked recessive disorder, females must inherit two copies of the recessive allele (one from each parent) because they possess two X chromosomes. One recessive allele makes the female a carrier with potentially no phenotypic expression of the disorder, but she can pass on the allele to her offspring. Sex-linked traits, therefore, appear more frequently in males who need only one copy of the recessive allele to express the disorder due to the presence of a single X chromosome.