MLL rearrangement in leukemic cells, normal BM, and fetal liver. Genomic DNA was digested with EcoRI, separated by electrophoresis, blotted to nylon membranes, and hybridized with the radiolabeled probes. (A) P/S4 probe. (B) 98.40 probe. RS4;11 cells were used as a positive control and normal peripheral lymphocytes served as a negative control. FL7 was isolated from a fetus age 19 gestational weeks. NBM4 was a BM sample from a normal infant BM donor age 6 months. UPN-PEDS no. 91 was a male age 17.7 years with newly diagnosed t(4;11) ALL. UPN-PEDS no. 5 was a female age 2.9 years with newly diagnosed normal diploid ALL. bp, base pairs.