X chromosome

From ArticleWorld

The X chromosome is one of the two sex chromosomes in several animal species. This chromosomes plays a role in the sex determination system for offspring. The other chromosome in mammals that plays a role in this system is the Y chromosome in the XY sex determination system. In normal sex determination in mammals, the females are XX and the males are XY. Thus the sex of the offspring is determined by if the X or the Y chromosome is derived from the male.

Diseases

This chromosome is associated with several genetic disorders or diseases. One of these is Klinefelter syndrome which is caused by the presence of extra copies of the X chromosome in males. This can affect male sexual development including testosterone levels and case mental retardation. Males with this disease usually have one extra copy of the X chromosome in each cell but there have been cases where there are up to three extra copies. There are also cases where there are extra copies of both the X and the Y chromosome.

Another disorder is the triple X syndrome. This is where females exhibit the condition of an extra X chromosome. Again, more than one extra copy of the X chromosome can occur but this is not common. The females with this condition tend to be slower learners with tall statures. Some may also be mentally retarded. Turner syndrome also concerns the X chromosome and is where the female has only one normal X chromosome or the other chromosome is completely missing. This results in short stature and infertility.

These conditions affect sex determination as well as sexual development and fertility.

Other conditions

Diseases caused by mutations of the X chromosome occur mainly in males as they only have one copy of the chromosome so even if the gene is recessive they exhibit the condition. In order to be affected females must receive the gene from both parents. If however the gene is passed to the female in a recessive nature there is still the risk of transmission to offspring. Some diseases known to be transmitted through X-linked recessive inheritance are color blindness and hemophilia.