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One of the human sex chromosomes. Females have two X chromosomes while males only have one.

Use in clinical context

Everybody has at least one X chromosome. One X chromosome is always inherited from the mother and, in females, a second is inherited from the father. This difference in the number of X chromosomes between the sexes results in different inheritance patterns of traits and conditions if the genetic variant responsible is found on the X chromosome. In particular, recessive variants on the X chromosome are always expressed in males as they only have one copy. However, in females where there are two copies of each gene, recessive variants on the X chromosome behave like autosomal recessive variants. This is why conditions such as colour blindness are more common in males than females.

Last updated on 31st May, 2019