X-linked recessive inheritance: Difference between revisions

Revision as of 20:31, 28 May 2008

Revision as of 00:21, 10 June 2008

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[[Image:XlinkRecessive.jpg|right|X-linked recessive inheritance]]

'''X-linked recessive''' is a mode of [[Mendelian inheritance|inheritance]] in which a mutation in a [[gene]] on the [[X chromosome]] causes the phenotype to be expressed (1) in males (who are necessarily [[Zygosity|homozygoushemizygous]] for the gene mutation because they have only one X chromosome) and (2) in females who are [[Zygosity|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|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. The current estimate of sequenced X-linked genes is 499 and the total including vaguely defined traits is 983<ref>[http://www.ncbi.nlm.nih.gov/Omim/mimstats.html OMIM X-linked Genes]</ref>