Question

males are more often affected by sex - linked traits than females because...
the presence of a y chromosome often worsens the effects of x - linked mutations.
males are hemizygous for the x chromosome.
sex - linked traits are located on autosomes that affect males more severely than females.
x chromosomes in males generally have more mutations than x chromosomes in females.

Explanation:

• Option 1: The Y chromosome does not worsen X - linked mutations. Sex - linked traits are mainly related to the X chromosome in this context.
• Option 2: Males have one X and one Y chromosome (XY). They are hemizygous for the X chromosome (only one copy). If there is a recessive mutation on the X chromosome, since there is no second X to potentially have a normal allele, the trait is expressed. Females have two X chromosomes (XX). For a recessive X - linked trait to be expressed in females, both X chromosomes need to have the recessive allele.
• Option 3: Sex - linked traits are not on autosomes. Autosomes are non - sex chromosomes. Sex - linked traits are on sex chromosomes (usually X).
• Option 4: There is no general rule that X chromosomes in males have more mutations than those in females. Mutation rates are not sex - specific in this way for X chromosomes.

Answer:

males are hemizygous for the X chromosome.