About Author: Rinki Verma (Research fellow)
Center of Experimental Medicine and Surgery,
Institute of Medical science
Banaras Hindu University
Varanasi - 221005
Abstract:
In 1965 , firstly fragility was reported in cells of a femeal previously irradiated and described as non-random human chromosome called “ Fragile sites” are heritable specific chromosome loci that exhibit an increased frequency of gaps, poor staining, constrictions or breaks when chromosomes are exposed to partial DNA replication inhibition. They constitute areas of chromatin that fail to compact during mitosis. They are classified as rare or common depending on their frequency within the population and are further subdivided on the basis of their specific induction chemistry into different groups differentiated as folate sensitive or non-folate sensitive rare fragile sites, and as aphidicolin, bromodeoxyuridine (BrdU) or 5-azacytidine inducible common fragile sites. Most of the known inducers of fragility share in common their potentiality to inhibit the elongation of DNA replication, particularly at fragile site loci. There are seven non-similar folate sensitive (FRA10A, FRA11B, FRA12A, FRA16A, FRAXA, FRAXE and FRAXF) and two non-folate sensitive (FRA10B and FRA16B) and have been molecularly characterized. Due to dynamic mutation formed DNA repeat sequences and involving the normally occurring polymorphic CCG/CGG trinucleotide repeats at the folate sensitive and AT-rich minisatellite repeats at the non-folate sensitive fragile sites. These rare fragile site FRAXA is the most important fragile site as it is associated with the fragile X syndrome significant to the clinical side and also explained the predisposition of tumors.
