pbl mutant cells fail to elongate during the segregation of abnormally long chromatids. (a) Time-lapse images of a pbl mutant cell expressing H2Av::RFP and I-CreI. The top panels are images of H2Av::RFP and the bottom panels are DIC images merged with H2Av signal (red). (b) Time-lapse images of a pbl mutant cell expressing H2Av::RFP (cyan) and myosin (red; see Video 6). The top panels are merges of H2Av and myosin signals. The bottom panels show one sagittal DIC image merged with H2Av signal (red). The broken lines show the contour of the cell. The cyan arrows point to the tip of the long chromatids. Time is given in minutes. Bars, 8 µm. (c) Scatter dot plot with mean ± SD showing the GMC elongation index for pbl mutant control cells or cells expressing I-CreI. n = number of cells. (d) Graph showing no linear correlation of the GMC elongation index with the length of the longest chromatid for pbl I-CreI cells. n = number of cells. (e) Scheme showing the scenarios that may arise in wild-type and pbl mutant cells with long chromatids. The wild-type cell adjusts its length to clear the long chromatid from the cleavage plane, hence producing euploid daughter cells, which will proliferate and differentiate properly. The pbl mutant cell fails to elongate in the presence of long chromatids. This produces aneuploid daughter cells, which will undergo apoptosis. (f) Images of wings from pbl mutant adult flies with our without I-CreI, heat shocked for 1 h at 37°C during the third instar larval stage. The pink arrows point to the wing morphological defects. (g) Histogram showing the frequency of adult flies exhibiting wings with morphological defects. n = number of experiments. N = total number of adult flies scored.