The Fragile X Chromosome

The Fragile X Chromosome

  • Submitted By: moshikudos
  • Date Submitted: 02/07/2010 3:30 PM
  • Category: Science
  • Words: 2384
  • Page: 10
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tic disorder that is caused by a break or weakness on the long arm of

the X chromosome (females have two X chromosomes and males have one X and one Y). The

gene where the break or weakness has occurred has been named FMR1 (Fragile X Mental

Retardation-1). Because of this defect, the gene cannot manufacture the protein that it normally

makes, which causes the features and characteristics of the syndrome. “Fragile X is estimated to

occur in 1 in 1,200 males and 1 in 2,500 females” (2). It occurs in all racial, ethnic, and

socioeconomic groups. It is said to be one of the most common genetic diseases and is the most

common inherited cause of learning disabilities and mental retardation known to exist.

Fragile X is, as mentioned above, inherited. Fathers who are carriers can only pass the affected

gene on to their daughters. The reason for this is that for males, the father always gives a Y

chromosome and the mother always gives an X chromosome (if the father gives an X

chromosome instead of a Y, the child would be female). Therefore, in order for the father to pass

the fragile X gene, the recipient would have to be a female. “Mothers who are carriers have a

50% chance of passing on the fragile X mutation to their children” (1). Females tend to be more

mildly affected by the fragile X gene than males because females have a second X chromosome

to compensate for the defective gene on the affected X chromosome. “It is estimated that 1 in

259 females, in the general population, can carry the fragile X mutation either as premutation or

full mutation” (3). Those with premutations are generally unaffected intellectually and of those

who carry the full mutation, approximately 50% will display a learning disability, intellectual

deficit, or mental retardation.

The underlying cause of Fragile X is a change in a single gene, the Fragile X Mental Retardation 1 (FMR1) gene, which is found on the X...

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