Definition
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.
Related terms
Autosomal inheritance | Chromosome | Recessive allele | X-linked inheritance | Y chromosome
