Editing X-linked recessive inheritance (section)

''Main Article'': <u>[[Sex linkage]]</u>{{short description|Mode of inheritance}}
[[File:X-linked recessive (2).svg|thumb|right|upright=1.75|X-linked recessive inheritance]]

'''X-linked recessive inheritance''' is a mode of [[Mendelian inheritance|inheritance]] in which a [[mutation]] in a [[gene]] on the [[X chromosome]] causes the [[phenotype]] to be always expressed in males (who are necessarily [[hemizygous]] for the gene mutation because they have one X and one [[Y chromosome]]) and in females who are homozygous for the gene mutation (see [[zygosity]]). Females with one copy of the mutated gene are carriers.

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]] (known as [[skewed X-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. The current estimate of sequenced X-linked genes is 499, and the total, including vaguely defined traits, is 983.<ref>{{cite web|url=https://www.ncbi.nlm.nih.gov/Omim/mimstats.html|title=OMIM X-linked Genes|website=nih.gov|access-date=3 May 2018|url-status=live|archive-url=https://web.archive.org/web/20160307090758/http://www.ncbi.nlm.nih.gov/Omim/mimstats.html|archive-date=7 March 2016}}</ref>