FISH with the 16p13 YAC probe on AML cells from patient 10 that contained the inv(16) (p13q22) abnormality. The chromosomal rearrangement is shown in the metaphase cell by the splitting of the hybridization signal between the p and q arm of the abnormal chromosome 16 while the normal chromosome retains only one signal. In the interphase cell this abnormality is detected by the presence of three fluorescent signals rather than the normal two. The 16p13 YAC probe was prepared and labeled with digoxigenin as described in Materials and Methods and detected with FITC-labeled anti-digoxigenin. The counterstain is propidium iodide (original magnification × 630).