A nonstaining gap of variable width that usually involves both chromatids and is always at exactly the same point on a specific chromosome derived from an individual or kindred. Such fragile sites are inherited in a Mendelian codominant fashion and exhibit fragility as shown by the production of acentric fragments and chromosome deletions. In cultured human cells, fragile sites are expressed when the cells are deprived of folate or thymidine or if methotrexate is added to the medium. See folic acid, fragile X–associated mental retardation. http://www.fraxa.org.
Subjects: Genetics and Genomics.