Sex linked

Concerning characteristics that are determined by genes carried on the sex chromosomes (on the X chromosome in particular).

Genes located on sex chromosomes

Sex linked is a trait in which a gene is located on a sex chromosome.

X-chromosome

In humans, the term generally refers to traits that are influenced by genes on the X chromosome. This is because the X chromosome is large and contains many more genes than the smaller Y chromosome.

Males affected more

In a sex-linked disease, it is usually males who are affected because they have a single copy of X chromosome that carries the mutation. In females, the effect of the mutation may be masked by the second healthy copy of the X chromosome.

Types

X-linked inheritance can be X-linked dominant or recessive.

X-linked dominant inheritance

X-linked dominant inheritance is a way a genetic trait or condition can be passed down from parent to child through mutations (changes) in a gene on a single X chromosome. In females (who have two X chromosomes), a mutation in a gene on one of the X chromosomes is enough to cause the condition. In males (who only have one X chromosome), a mutation in the copy of the gene on the single X chromosome causes the condition. Fathers cannot pass X-linked dominant conditions to their sons, but all daughters of affected fathers will be affected with the condition and can pass it on to their children.

X-linked recessive inheritance

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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