What is X-Chromosome?

May 22, 2024

Scientists have found a molecular link between altered X-chromosome inactivation and autoimmune diseases.

About X-Chromosome:

  • It is one of the two sex chromosomes in humans (the other is the Y chromosome). 
    • There are 23 pairs of chromosomes in the human body. This includes 22 pairs of autosomal or somatic chromosomes that are common to both men and women and one chromosome that differs according to what gender a person is (sex chromosomes).
  • Each person usually has one pair of sex chromosomes in each cell. Females typically have two X chromosomes, while males typically have one X and one Y chromosome.
  • Men inherit the X chromosome they have from their mother and the Y chromosome from their father, while women inherit one X chromosome from the mother and the other from the father.
  • In women, the X chromosome represents almost 5% of the total DNA, and in men, who have only one X chromosome, it represents about 2.5% of the total DNA.
  • Early in the embryonic development of people with two X chromosomes, one of the X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or lyonization.
    • X-inactivation ensures that people with two X chromosomes have only one functional copy of the X chromosome in each cell.
    • Because X-inactivation is random, normally, the X chromosome inherited from one parent is active in some cells, and the X chromosome inherited from the other parent is active in other cells.
  • The X chromosome likely contains 900 to 1,400 genes that provide instructions for making proteins. 
  • Genetic disorders that arise from missing, additional, or malformed copies of the X chromosome are termed numerical disorders.
    • Examples include Klinefelter’s syndrome, where a male has one or more extra copies; Triple X syndrome, where a female has one extra copy and Turner syndrome, where a female has one normal X chromosome and one missing or abnormal one.