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''Main Article:'' <u>[[Sex linkage]]</u>{{short description|Mode of inheritance}}
{{refimprove|date=September 2009}}
[[File:X-linked dominant.svg|thumb|upright=1.75|X-linked dominant inheritance]]
'''X-linked dominant inheritance''', sometimes referred to as '''X-linked dominance''', is a mode of [[
X-linked dominant traits do not necessarily affect males more than females (unlike [[X-linked recessive]] traits). The exact pattern of inheritance varies, depending on whether the father or the mother has the trait of interest. All
==Genetics==
As the X chromosome is one of the [[sex chromosome]]s (the other being the [[Y chromosome]]), X-linked inheritance is determined by the [[sex]] of the parent carrying a specific gene and can often seem complex. This is due to the fact that, typically, [[female]]s have two copies of the X-chromosome, while [[male]]s have only one copy. The difference between [[Dominance (genetics)#Dominant trait|dominant]] and [[Dominance (genetics)#Recessive|recessive]] inheritance patterns also plays a role in determining the chances of a child inheriting an X-linked disorder from their parentage.{{fact|date=January 2018}}▼
▲inheritance is determined by the [[sex]] of the parent carrying a specific gene and can often seem complex. This is due to the fact that, typically, [[female]]s have two copies of the X-chromosome, while [[male]]s have only one copy. The difference between [[Dominance (genetics)#Dominant trait|dominant]] and [[Dominance (genetics)#Recessive|recessive]] inheritance patterns also plays a role in determining the chances of a child inheriting an X-linked disorder from their parentage.
X-linked dominant disorders tend to affect females more often because they tend to be developmentally fatal in males. This is because males have only one copy of X-chromosome while females have two copies.{{fact|date=January 2018}}
===Inheritance===
In X-linked dominant inheritance, when the mother alone is the [[genetic carrier|carrier]] of a mutated, or defective gene associated with a disease or disorder; she herself will have the disorder. Her children will inherit the disorder as follows:
* Of her daughters and sons: 50% will have the disorder, 50% will be completely unaffected. Children of either sex have an even chance of receiving either of their mother's two X chromosomes, one of which contains the defective gene in question.▼
▲*Of her daughters and sons: 50% will have the disorder, 50% will be completely unaffected. Children of either sex have an even chance of receiving either of their mother's two X chromosomes, one of which contains the defective gene in question.
When the father alone is the carrier of a defective gene associated with a disease or disorder, he too will have the disorder. His children will inherit the disorder as follows:
* Of
* Of his
If both parents were carriers of a defective gene associated with a disease or disorder, they would both have the disorder. Their children would inherit the disorder as follows:
* Of their daughters: 100% will have the disorder, since all of the daughters will receive a copy of their father's X chromosome.
* Of the sons: 50% will have the disorder, 50% will be completely unaffected. Sons have an equal chance of receiving either of their mother's X chromosomes.▼
In such a case, where both parents carry and thus are affected by an X-linked dominant disorder, the chance of a daughter receiving two copies of the X chromosome with the defective gene is 50%, since daughters receive one copy of the X chromosome from both parents. Were this to occur with an X-linked dominant disorder, that daughter would likely experience a more severe form.▼
▲*Of their daughters: 100% will have the disorder, since all of the daughters will receive a copy of their father's X chromosome.
▲*Of the sons: 50% will have the disorder, 50% will be completely unaffected. Sons have an equal chance of receiving either of their mother's X chromosomes.
Some X-linked dominant conditions such as [[Aicardi
▲In such a case, where both parents carry and thus are affected by an X-linked dominant disorder, the chance of a daughter receiving two copies of the X chromosome with the defective gene is 50%, since daughters receive one copy of the X chromosome from both parents. Were this to occur with an X-linked dominant disorder, that daughter would likely experience a more severe form.
A few scholars have suggested discontinuing the use of the terms ''dominant'' and ''recessive'' when referring to X-linked inheritance, 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.<ref name="pmid15316978">{{cite journal|vauthors=Dobyns WB, Filauro A, Tomson BN, Chan AS, Ho AW, Ting NT, Oosterwijk JC, Ober C|date=August 2004|title=Inheritance of most X-linked traits is not dominant or recessive, just X-linked|journal=American Journal of Medical Genetics. Part A|volume=129A|issue=2|pages=136–43|doi=10.1002/ajmg.a.30123|pmid=15316978}}</ref>
▲Some X-linked dominant conditions such as [[Aicardi Syndrome]] are fatal to boys, therefore only girls with these conditions survive, or boys with [[Klinefelter's syndrome]] (and hence have more than one X chromosome).
==List of dominant X-linked diseases==
* [[Vitamin D]] resistant [[rickets]]: [[X-linked hypophosphatemia]]
* [[Rett syndrome]] (95% of cases are due to sporadic mutations(not inherited))
* Most cases of [[Alport syndrome]]<ref name=pmid14514738>{{cite journal | vauthors = Jais JP, Knebelmann B, Giatras I, De Marchi M, Rizzoni G, Renieri A, Weber M, Gross O, Netzer KO, Flinter F, Pirson Y, Dahan K, Wieslander J, Persson U, Tryggvason K, Martin P, Hertz JM, Schröder C, Sanak M, Carvalho MF, Saus J, Antignac C, Smeets H, Gubler MC | display-authors = 6 | title = X-linked Alport syndrome: natural history and genotype-phenotype correlations in girls and women belonging to 195 families: a "European Community Alport Syndrome Concerted Action" study | journal = Journal of the American Society of Nephrology | volume = 14 | issue = 10 | pages = 2603–10 | date = October 2003 | pmid = 14514738 | doi = 10.1097/01.ASN.0000090034.71205.74 | doi-access = free | hdl = 2078.1/40773 | hdl-access = free }}</ref>
* [[Incontinentia pigmenti]]<ref>{{cite web | url = http://dermnetnz.org/systemic/incontinentia-pigmenti.html | title = Incontinentia pigmenti | first = Vanessa | last = Ngan | name-list-style = vanc | publisher = DermNet NZ | date = 2005 }}</ref><ref>{{EMedicine|article|1114205|Incontinentia Pigmenti}}</ref>
* [[Giuffrè–Tsukahara syndrome]]<ref name=
* [[Goltz syndrome]]
* X-linked dominant [[porphyria]]<ref name=pmid24131146>{{cite journal | vauthors = Seager MJ, Whatley SD, Anstey AV, Millard TP | title = X-linked dominant protoporphyria: a new porphyria | journal = Clinical and Experimental Dermatology | volume = 39 | issue = 1 | pages = 35–7 | date = January 2014 | pmid = 24131146 | doi = 10.1111/ced.12202 }}</ref>
▲*[[Fragile X syndrome]]
== See also ==
* [[Sex linkage]]▼
* [[X-linked recessive inheritance]]▼
▲*[[Rett syndrome]]
▲*[[Sex linkage]]
▲*[[X-linked recessive inheritance]]
== References ==
{{reflist|32em}}
{{X-linked disorders}}
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