In humans, males have only one copy of the X chromosome in their cells. Therefore, human males express all the X-linked genes present on their X chromosomes irrespective of the recessive or dominant nature of the allele. This occurs since males do not have one more copy of the X chromosome to carry another allele for the gene. So, all the X-linked alleles present on the X-chromosomes of the human males are expressed.
For example, human males with genotype X^cY and X^hY express colorblindness and hemophilia respectively. Though, human females express these recessive X-linked disorders in homozygous genotype only.
