High Quality Content by WIKIPEDIA articles! X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed (1) in males (who are necessarily hemizygous for the gene mutation because they have only one X chromosome) and (2) in females who are homozygous for the gene mutation (i.E., they have a copy of the gene mutation on each of their two X chromosomes). X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. FEmales have two X chromosomes, while males have one X and one Y chromosome. CArrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other.