Southern blot analysis demonstrating multiple copies of the MLL gene in t-AML of patient RUPN 84 and cell line 2L1.BamHI- and HindIII-digested DNAs were hybridized separately with MLL bcr cDNA and SCL genomic probes (A). Although the patient received DNA topoisomerase II-targeted chemotherapy and had monoblastic leukemia, the MLL gene was not rearranged. HindIII-digested DNAs were hybridized simultaneously with MLL bcr cDNA and SCL genomic probes to assess equivalence in loading (B). The bold arrow in (B) indicatesMLL signals; the thin arrow indicates SCL signals. The increased MLL signal intensity compared with PBMC control, 4.3:1 when normalized for loading by hybridization with SCLprobe, is consistent with approximately 8 to 9 copies of theMLL gene in the t-AML and cell line 2L1.