X chromosome

Last reviewed 01/2018

Sex linked disorders are due to alterations in the normal sex chromosomes of the sufferer.

Normally, the female complement is two X sex chromosomes. One is derived from each parent and one of the pair is also randomly inactivated by a process called lyonization at an early developmental stage.

In contrast, a male has the XY sex chromosome constitution and so has only one copy of each X-linked gene. The Y chromosome contains important male determinants.

The family pedigree of sex-linked disorders depends on which sex chromosome carries the mutant gene, and whether the trait is dominant or recessive. Some autosomal traits may mimic sex-linked diseases.