Furthermore, we show that INCENP is recruited to the DRT/DMC chromosomes during all phases of mitosis.     ///    "Finally, cells with DRT/DMC chromosomes have centrosome amplification, abnormal spindle assembly, endoreduplication and significant chromosome instability.. "    ///    "In contrast, Aurora B kinase is absent on DRT/DMC chromosomes when these chromosomes lack serine 10 phosphorylation of H3. "    ///    "In this report, we show that chromosomes with DRT/DMC contain phosphorylated Chk1, consistent with activation of the S-M phase checkpoint. "    ///    "We also show that mitotic arrest deficient 2 (Mad2), a member of the spindle assembly checkpoint, is present on DRT/DMC chromosomes at a time when the normally condensed chromosomes show no Mad2 staining, indicating that DRT/DMC activates the spindle assembly checkpoint. "    ///    DRT/DMC chromosomes are common in tumor cells in vitro and in vivo and occur frequently in cells exposed to ionizing radiation. 