Do X-linked dominant traits affect males or females more?
A greater proportion of females should be affected because they have two X chromosomes while males only have one. Since only one X-linked dominant gene is needed to produce the trait, females should show the trait twice as frequently as males because they have two opportunities to pick up the gene for a given gene frequency in the population. On the other hand, the degree to which the trait is expressed may actually be lower in females due to random X-inactivation in all females. (i.e. only about half the cells might actually express the gene). Furthermore, if the proportion of cells that undergo X-inactivation in the female are randomly skewed toward inactivation of the X chromosome with the dominant gene, the expression of the resulting dominant phenotype will be even less, and vice-versa.
