To rule out the possibility that the reason Runx1+/R188QMx1-CreCbfb+/56M mice did not develop leukemia was because of RUNX1 haploinsufficiency, we examined Runx1+/fMx1-CreCbfb+/56M mice, in which one Runx1 allele can be deleted by Cre. This evidence concerns the gene RUNX1 and leukemia.