Final answer:
Sex-linked traits are more common in males because they are hemizygous for the X chromosome, expressing the recessive X-linked allele they inherit. Females, with two X chromosomes, must inherit two recessive alleles to express the trait.
Step-by-step explanation:
Sex-linked traits are more common in males than in females due to the differences in the sex chromosomes they possess. Males have one X and one Y chromosome, making them hemizygous for the genes on the X chromosome. This means that if a male inherits a recessive X-linked allele, he will express the trait because there is no corresponding allele on the Y chromosome. In contrast, females have two X chromosomes, so they must inherit two copies of the recessive allele to express the recessive trait. If they inherit only one, they become carriers of the trait without necessarily expressing it. This carrier status allows them to pass on the recessive trait to half of their daughters and all of their sons, who will express the trait if they inherit the recessive allele.
Conditions such as red-green color blindness, hemophilia, and muscular dystrophy are examples of X-linked recessive disorders that appear more frequently in males. Females can only express these X-linked disorders if they receive two recessive alleles, one from each parent.