X linked

X-linked inheritance is a mode of genetic inheritance by which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (who are necessarily hemizygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation.

Genetics

X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes, while males have one X and one Y chromosome. The current estimate of sequenced X-linked genes is 499 and the total including vaguely defined traits is 983.

X-linked recessive inheritance

In X-linked recessive inheritance, a female who is a carrier of a mutation can have affected or unaffected sons, or carrier or non-carrier daughters, depending on whether the sons or daughters receive the X chromosome carrying the mutation. The probability is 50% for each child. Affected sons are usually isolated in the family tree because they receive the X chromosome that carries the mutation from their carrier mother.

X-linked dominant inheritance

In X-linked dominant inheritance, a mutation in a gene on the X chromosome causes the phenotype to be expressed (1) in males (who are necessarily hemizygous for the gene mutation because they have one X and one Y chromosome) and (2) in females who are homozygous for the gene mutation (i.e., they have a copy of the gene mutation on each of their two X chromosomes).

See also

• Genetics
• Chromosome
• Mutation
• Phenotype
• Homozygous
• Hemizygous

X linked Resources
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