https://en.wikipedia.org/wiki/Sex_linkage https://en.wikipedia.org/wiki/Sex_linkage > X-linked recessive traits are expressed in all heterogametics, but are on

https://en.wikipedia.org/wiki/Sex_linkage https://en.wikipedia.org/wiki/Sex_linkage > X-linked recessive traits are expressed in all heterogametics, but are only expressed in those homogametics that are homozygous for the recessive allele. For example, an X-linked recessive allele in humans causes haemophilia, which is much more common in males than females because they are hemizygous (see zygosity) and therefore express the trait when they inherit one mutant allele. In contrast, a female must inherit two mutant alleles, a less frequent event since the mutant allele is rare in the population.