Fig. 2. Tumour incidence in Mll–lacZ mice. Tumour incidence was monitored in cohorts of mice and when signs of indolence or unhealthy coat appeared, animals were killed and post-mortems carried out. (A) Data showing incidence of Mll–lacZ mice with detectable tumours compared with a cohort of Mll–myc tag mice (plotted as numbers of mice with time in months). The cohort size of the Mll–lacZ mice was 43 and that of the Mll–myc tag mice was 27. (B) Data showing the incidence of AML versus ALL within cohorts of Mll–lacZ and Mll–myc tag mice. Distinct forms of disease were found to be AML or ALL and lymphoma in the groups of mice as indicated. (C) Southern filter hybridization of DNA from Mll–lacZ chimeric animals with acute leukaemia. DNA was prepared from the spleen of the chimeras indicated (1–6 and 8–11 diagnosed with AML and 13 and 37 diagnosed with ALL), or chimeras not afflicted with discernible disease (17, 22, 23 and 21). DNA was digested with BglII, separated on 0.8% agarose alongside 129 liver DNA and DNA from Mll–lacZ ES clone 14, both digested with BglII. After transfer to nylon membranes, hybridization was carried out with ³²P-labelled probe 1.5RXT2. The upper band represents the targeted allele (found in clone 14) and the lower band represents the germ-line allele. (D) Southern filter hybridization of DNA from Mll–myc tag chimeric animals with acute leukaemia. DNA was prepared from the spleen of the chimeras indicated (2026, 2020, 2010 diagnosed with AML) digested with KpnI, separated on 0.8% agarose alongside 129 liver DNA and DNA from an Mll–myc tag heterozygous mouse. After transfer to nylon membranes, hybridization was carried out with ³²P-labelled probe BB (3′ Mll probe). The upper band represents the targeted allele (found in clone 14) and the lower band represents the germ-line allele.