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.
For example, an X-linked recessive allele in humans causes haemophilia. Haemophilia is much more common in males than females because males are hemizygous-they only have one copy of the gene in question-and therefore express the trait when they inherit one mutant allele.