Question

Why is fragile X more common in males even though it is X-chromosome linked?

a) Males have a second Y chromosome
b) Females have two X chromosomes
c) Males have weaker immune systems
d) Females lack the gene responsible for fragile X

Answer 1

Fragile X is more common in males because males have only one X chromosome, while females have two X chromosomes. This means that recessive X-linked alleles are always expressed in males, while females must inherit two copies of the recessive allele to express the trait.

Step-by-step explanation:

Because males have just one X chromosome, they have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. Because females have two X chromosomes, they have two alleles for any X-linked trait. Therefore, they must inherit two copies of the recessive allele to express the recessive trait. This explains why X-linked recessive traits are less common in females than males.