FIG 2.

Common and rare fragile sites. (A) The common FRA3B fragile site. Complete and incomplete L1 retrotransposons are shown by blue and purple arrows, respectively. Vertical dotted arrows indicate known deletion junctions, whose extents are shown by horizontal dashed lines, as heterozygous or homozygous deletions, in five cancer cell lines in which they were mapped. (Based on data from reference 51.) (B) The common FRA16D fragile site. AT-rich sequences are indicated by vertical pink arrows, with the darker shade corresponding to a higher flexibility index. Vertical dotted arrows indicate known deletion junctions, whose extents are shown by horizontal dotted lines, in two cancer cell lines in which they were mapped. (Based on data from reference 50.) (C) The rare FRA16B fragile site. It contains three AT-rich minisatellites, shown by green arrows. The most telomeric repeat is unstable, and its expansion triggers fragile site expression (58). (D) The rare FRA10B fragile site. It contains five AT-rich minisatellites, shown by green arrows. The internal repeat is unstable and prone to expansions. (Based on data from reference 59.)