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