X-linked recessive inheritance: Difference between revisions

Revision as of 17:22, 9 June 2020

Revision as of 17:34, 9 June 2020

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{{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 [[homozygous]] 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.

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== Patterns of Inheritance ==

In humans, inheritance of X-linked recessive traits follows a unique pattern made up of three points. The first is that affected fathers cannot pass x-linked recessive traits to their sons because fathers give Y chromosomes to their sons. This means that males affected by an x-linked recessive disorder inherited the responsible X chromosome from their mothers. Second, x-linked recessive traits are more commonly expressed in males than females.<ref>{{Cite web|last=|first=|date=8 July 2009|title=Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals|url=https://www.ncbi.nlm.nih.gov/books/NBK115561/|url-status=live|archive-url=|archive-date=|access-date=9 June 2020|website=National Center for Biotechnology Information}}</ref> This is due to the fact that males only possess a single X chromosome, and thus only require one mutated X in order to be affected. Women posses two X chromosomes, and thus must receive two of the mutated recessive X chromosomes (one from each parent). A popular example showing this pattern of inheritance is that of the descendants of Queen Victoria and the blood disease hemophilia.<ref>{{Cite web|date=2014-03-04|title=History of Bleeding Disorders|url=https://www.hemophilia.org/Bleeding-Disorders/History-of-Bleeding-Disorders|access-date=2020-06-09|website=National Hemophilia Foundation|language=en}}</ref> The last pattern seen is that x-linked recessive traits tend to skip generations, meaning an affected grandfather will not have an affected son, but could have an affected grandson through his granddaughter.<ref>{{Cite book|last=Pierce|first=Benjamin A.|title=Genetics: A Conceptual Approach|publisher=Macmillan Learning|year=2020|isbn=978-1-319-29714-5|pages=154-155154–155}}</ref> Explained further, all daughters of an affected man will obtain his mutated X, and will then be either carriers or affected themselves depending on the mother. The resulting sons will either have a 50% chance of being affected (mother is carrier), or 100% chance (mother is affected). It is because of these percentages that we see males more commonly affected than females.

== Push Back on Recessive/Dominant Terminology ==

A few scholars have suggested discontinuing the use of the terms ''dominant'' and ''recessive'' when referring to X-linked inheritance.<ref name=":0">{{cite journal|last1=Dobyns|first1=William B.|last2=Filauro|first2=Allison|last3=Tomson|first3=Brett N.|last4=Chan|first4=April S.|last5=Ho|first5=Allen W.|last6=Ting|first6=Nicholas T.|last7=Oosterwijk|first7=Jan C.|last8=Ober|first8=Carole|year=2004|title=Inheritance of most X-linked traits is not dominant or recessive, just X-linked|journal=American Journal of Medical Genetics|volume=129A|issue=2|pages=136|doi=10.1002/ajmg.a.30123|pmid=15316978}}</ref> The possession of two X chromosomes in females leads to dosage issues which are alleviated by [[X-inactivation]]. <ref>{{Cite journal|last=Shvetsova|first=Ekaterina|last2=Sofronova|first2=Alina|last3=Monajemi|first3=Ramin|last4=Gagalova|first4=Kristina|last5=Draisma|first5=Harmen H. M.|last6=White|first6=Stefan J.|last7=Santen|first7=Gijs W. E.|last8=Chuva de Sousa Lopes|first8=Susana M.|last9=Heijmans|first9=Bastiaan T.|last10=van Meurs|first10=Joyce|last11=Jansen|first11=Rick|date=March 2019-03|title=Skewed X-inactivation is common in the general female population|url=https://www.nature.com/articles/s41431-018-0291-3|journal=European Journal of Human Genetics|language=en|volume=27|issue=3|pages=455–465|doi=10.1038/s41431-018-0291-3|issn=1476-5438}}</ref> Stating that the highly variable penetrance of X-linked traits in females as a result of mechanisms such as skewed X-inactivation or [[somatic mosaicism]] is difficult to reconcile with standard definitions of dominance and recessiveness, scholars have suggested referring to traits on the x chromosome simply as ''X-Linked.''<ref name=":0" />

==Examples==