Multiple emergence of leukemic clones in Cdkn1b^+/−/MTCP1^TG mice. (A) The presence of clonal populations was detected by CDR3 spectratyping. Examples of chromatograms are shown for different mice from the 4 genotypes, and different Vβ segments used for Tcrb rearrangements. Black rectangles indicate signal saturation. Arrows indicate rearrangements fulfilling criteria for clonality. DM indicates Cdkn1b^+/−/MTCP1^TG; Tg, MTCP1 transgenics; Htz, Cdkn1^+/−; and WT, wild type. (B) Summary of spectratyping data from the 14 mice tested. P indicates polyclonal pattern; C, clonal pattern; U, unknown, no significant signal; and NA, not available.