chromosome X

The X chromosome represents approximately 5% of the total DNA in cells.

  • Human females have two copies of this chromosome whereas human males have one copy of chromosome X and one copy of chromosome Y. To compensate the higher gene dose of the two X chromosomes, early in embryonic development in females, the most genes of one copy of the X chromosomes are inactivated in somatic cells (cells other than egg and sperm cells).
  • About 10% of all hereditary diseases are documented for the X chromosome. Additionally a lot of genes of chromosome X are only expressed in the brain. A mutation in one of these genes often causes mental defects.

Summary:

Gene examples of chromosome X:

  • sex chromosome
  • about 155.000.000 base pairs
  • about 1336 genes

 

The genes OPN1LW and OPN1MW encodes long-wavelength- and middle-wavelength-sensitive photopigments in the cones (specialized cells for the detection of light and color) of the retina (a light-sensitive tissue that lines the back of the eye). Mutations in these genes cause colour vision deficiency.

The F8 gene carries instructions for the coagulation factor VIII, which is required for normal blood clotting. Defects in this gene results in hemophilia A (blood clots can't form properly in response to injury, leading to excessive bleeding).

chromosome overview (scaled down):
overview chromosome X
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)
Legend:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
not yet determined (N)