Question

why do recessive x - linked traits occur more frequently and with greater severity in human males than in human females?
check all that apply
males have an x chromosome, but females typically do not.
males typically have two y chromosomes, so they never receive a dominant allele carried on an x chromosome.
males dont have a second x chromosome to mask the effects of the first one.
in males, x inactivation shuts off expression of the alleles on one x chromosome.
only females who inherit two x - linked recessive alleles fully express the recessive phenotype.
sperm are more likely to carry an x chromosome than a y chromosome.

Explanation:

• Males have an X chromosome, but females typically do not: Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). So males have an X chromosome, and females have two. This statement is correct as it explains the chromosomal basis.
• Males don't have a second X chromosome to mask the effects of the first one: Since males have only one X chromosome (XY), if there is a recessive allele on that X, there is no second X with a dominant allele to mask it. Females (XX) can have a dominant allele on one X to mask a recessive on the other. This is a key reason for more severe and frequent X - linked recessive traits in males.
• Only females who inherit two X - linked recessive alleles fully express the recessive phenotype: Females need two copies of the recessive allele (one on each X) to express the recessive phenotype. Males, with only one X, express the trait if they have the recessive allele on their single X. This is also a valid point related to the expression of X - linked recessive traits.

Answer:

Males have an X chromosome, but females typically do not; Males don't have a second X chromosome to mask the effects of the first one; Only females who inherit two X - linked recessive alleles fully express the recessive phenotype.