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== Inheritance ==
In medicine, X-linked dominant inheritance indicates that a gene responsible for a [[genetic disorder]] is located on the X chromosome, and only one copy of the gene is sufficient to cause the disorder when inherited from a parent who has the disorder.
As the X chromosome is one of the [[sex chromosome]]s (the other being the [[Y chromosome]]), X-linked
inheritance is determined by the [[gender]] 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.
{| class=wikitable border=0 cellpadding=3 cellspacing=0 align=right width=400
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| align=right valign=bottom|[[Image:Xlink dominant mother.jpg|thumb|175px]] || align=left valign=bottom|[[Image:X-link dominant father.jpg|thumb|175px]]
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| align=center colspan=2 valign=top|<small>X-linked dominant inheritance works differently depending upon whether the mother (left image) or father (right image) is the carrier of a gene that causes a disease or disorder.</small>
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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 both genders have an even chance of receiving either of their mother's two X chromosomes, one of which contains the defective gene in question.
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| <gallery>Image:Xlink dominant mother.jpg</gallery>
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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 his daughters: 100% will have the disorder, since all of his daughters will receive one copy of his single X chromosome.
*Of his sons: none will have the disorder; sons do not receive an X chromosome from their father.
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| <gallery>Image:X-link dominant father.jpg</gallery>
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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.
Some X-linked dominant conditions such as [[Aicardi Syndrome]] are fatal to boys, therefore only girls with these conditions survive. Similarly, individuals with [[Klinefelter's Syndrome]] are referred to as "47,XXY Males".
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