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X-linked recessive inheritance

(…. linkt reh-SEH-siv in-HAYR-ih-tunts)
X-linked recessive inheritance refers to genetic conditions associated with mutations in genes on the X chromosome. A male carrying such a mutation will be affected, because he carries only one X chromosome. A female carrying a mutation in one gene, with a normal gene on the other X chromosome, is generally unaffected.
Drawing showing an X-linked recessive inheritance pattern between a father, mother, and their children. The panel on the left shows an affected father (who only has one X chromosome) with a mutated (changed) gene on the X chromosome; an unaffected mother (who has two X chromosomes) with a normal gene on both X chromosomes; an unaffected daughter (carrier), who has two X chromosomes, with a mutated gene on one X chromosome and a normal gene on the other X chromosome; and an unaffected son (who only has one X chromosome) with a normal gene on the X chromosome. The panel on the right shows an unaffected father with a normal gene on the X chromosome; an affected mother (carrier) with a normal gene on one X chromosome and a mutated gene on the other X chromosome; an unaffected daughter with a normal gene on both X chromosomes; an unaffected son with a normal gene on the X chromosome; an unaffected daughter (carrier) with a mutated gene on one X chromosome and a normal gene on the other X chromosome; and an affected son with a mutated gene on the X chromosome.Enlarge this image in new window
X-linked recessive inheritance is a way a genetic trait or condition can be passed down from parent to child through mutations (changes) in a gene on the X chromosome. In males (who only have one X chromosome), a mutation in the copy of the gene on the single X chromosome causes the condition. Females (who have two X chromosomes) must have a mutation on both X chromosomes in order to be affected with the condition. If only the father or the mother has the mutated X-linked gene, the daughters are usually not affected and are called carriers because one of their X chromosomes has the mutation but the other one is normal. Sons will be affected if they inherit the mutated X-linked gene from their mother. Fathers cannot pass X-linked recessive conditions to their sons.
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