MEK1act increased mitotic spindle defects and genomic instability in MCH603 cells. A, Flow cytometry analysis of cell DNA content. B, Chromosome ploidy analysis of MCH603 and MCH603MEK1act cells. Bars indicate 2 μM. a, Pseudodiploid M-phase spread of an MCH603 cell; b, Polyploid and metaphase spreads of MCH603MEK1act cells, with one showing an anaphase bridge (arrow head); and c, lack of cytokinesis in MCH603MEK1act cell. C, Ploidy variations in mitotic cells of HT1080 and its variants. Values represent the percentages of diploid and polyploid cells in 400 total cells of each cell line.