Fig. 1. FISH staining on anaphase human primary fibroblasts (MRC-5 cells) recovering from a nocodazole-induced mitotic arrest. Alphoid-specific probes for chromosome 7 (FITC, yellow) and 11 (Rhodamine, red) were used. DNA was stained by DAPI (blue). (A) Normal distribution of chromosome 7 and 11 at spindle poles. (B) Loss of a single chromatid of chromosome 7. (C) Loss of both sister chromatids of chromosome 7. When both sisters are lost in anaphase cells, their kinetochores are frequently separated and only in a few cases are the two chromatids still connected at the kinetochore level as shown in D for chromosome 11. The graph below shows quantitative results of the in situ hybridization analysis on 6378 anaphases, of which 94 displayed lagging chromosomes, for a total of 130 chromosome loss events for the two chromosomes under study. The data show that single lagging chromatids are the great majority of loss events. Bar, 5 µm.