X-linked recessive inheritance

Main Article: <a href="/facts/Sex_linkage/buXJkWJg">Sex linkage</a>

X-linked recessive inheritance is a mode of <a href="/facts/Mendelian_inheritance/v2038wkl">inheritance</a> in which a <a href="/facts/Mutation/Ee4NnWbY">mutation</a> in a <a href="/facts/Gene/e1swwPY6">gene</a> on the <a href="/facts/X_chromosome/hpJxhSUr">X chromosome</a> causes the <a href="/facts/Phenotype/vxWXKGLj">phenotype</a> to be always expressed in males (who are necessarily <a href="/facts/Hemizygous/XzEJ5gPp">hemizygous</a> for the gene mutation because they have one X and one <a href="/facts/Y_chromosome/nBDd0Vlg">Y chromosome</a>) and in females who are homozygous for the gene mutation (see <a href="/facts/Zygosity/XzEJ5gPp">zygosity</a>). Females with one copy of the mutated gene are carriers.
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 <a href="/facts/Y_chromosome/nBDd0Vlg">Y chromosome</a>. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in <a href="/facts/X-chromosome_inactivation/wMWHzvcw">X-chromosome inactivation</a> (known as <a href="/facts/Skewed_X-inactivation/lFjlwRHg">skewed X-inactivation</a>) can lead to varying degrees of clinical expression in carrier females, since some cells will express one X <a href="/facts/Allele/8FxCS9KA">allele</a> and some will express the other. The current estimate of sequenced X-linked genes is 499, and the total, including vaguely defined traits, is 983.

X-linked recessive inheritance open-in-new

X-linked recessive inheritance