Since only 31% of the E1A/Ras Hipk2−/− MEFs undergo cytokinesis failure (Figure 1C), we reasoned that if aneuploidy and CIN do not significantly contribute to the tumorigenicity of these MEFs, the karyotype-defective cells would have been counter selected in favor of the cells that succeed in faithful cytokinesis. This evidence concerns the gene HIPK2 and aneuploidy.