Fluorescence in situ hybridization to visualize etoposide-induced chr11 rearrangements in cells after long recovery period. (A) Schematic overlap between fluorescent probes of 11q23 locus–specific identifier (LSI). Intact 11q23 is seen as yellow signal (overlap of green and red). Aberration of 11q23 is seen as separation of probes into independent green and red signals. (B-E) Whole chromosome painting with chr 11–Cy3 (red) and chr 4–FITC (green). (B) Untreated CD34⁺ control. (C-E) Representative metaphase spreads that contain chr 11 aberrations. (F-I) LSI of chromosome band 11q23 in interphase and metaphase cells. (F,J) Untreated CD34⁺ control. (G-H) Representative split signals observed in 59 of 850 etoposide-treated and analyzed cells. (I, K-M) Representative complex rearrangements observed in 46 of 850 etoposide-treated and analyzed cells. Images were viewed at 600×, 1.4 aperture, with Immersol oil immersion (Zeiss, Oberkochen, Germany).