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Definition of Fragile X chromosome

Fragile X chromosome: An X chromosome with a heritable fragile site associated with a frequent form of mental retardation -- the fragile X syndrome.

The fragile X chromosome was first sighted by Dr. Herbert A. Lubs in 1969 who termed it the "marker X.". The fragile X is also called FRAXA. It was the first fragile site found on the X chromosome.

The fragile X chromosome is due to a trinucleotide repeat sequence (a recurring motif of 3 bases) in the DNA at that spot.

Source: MedTerms™ Medical Dictionary
http://www.medicinenet.com/script/main/art.asp?articlekey=3516
Last Editorial Review: 8/28/2013

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