Question

why are more males than females affected by x - linked recessive genetic diseases?
○ females have two y chromosomes and cannot be affected by x - linked traits.
○ females have an additional y chromosome to mask the x - linked recessive allele.
○ males have a y chromosome that cannot mask the x - linked recessive allele.
○ males and females are affected equally by x - linked recessive genetic conditions.
○ females have no y chromosome to mask the x - linked recessive allele.

Explanation:

In humans, females have two X chromosomes (\(XX\)), while males have one X and one Y chromosome (\(XY\)). For X - linked recessive genetic diseases, if a male inherits a recessive allele on the X chromosome, since the Y chromosome does not have an equivalent locus to mask the recessive allele on the X chromosome, the male will express the disease. Females, with two X chromosomes, need to inherit the recessive allele on both X chromosomes (a less likely event) to express the X - linked recessive disease. Option A is wrong as females have no Y chromosomes. Option B is incorrect because females have no Y chromosomes to mask alleles. Option D is wrong as males and females are not equally affected. Option E is incorrect as it is the presence of a non - masking Y in males (not the absence of Y in females) that leads to more male - affected cases for X - linked recessive diseases.

Answer:

C. Males have a Y chromosome that cannot mask the X - linked recessive allele.