Increased clonogenic progenitors in JAK2^V617F mice. Colony assays were performed 6 and 26 weeks after pIpC. (A) Megakaryocyte colonies (CFU-MK). (B) Granulocyte-macrophage colonies (CFU-GM). (C) Erythroid colonies (BFU-E). *P < .05. **P < .01. Data are mean ± SEM. (D) PCR analysis of individual BFU-E and CFU-GM colonies from mice 26 weeks after pIpC using primers P1 + P2 + P5 (see Figure 1A). No colonies were homozygous for the recombined allele. Vertical line has been inserted to indicate removal of a gel lane. Lanes 1 to 11 indicate individual colonies; +ve, ES cell clone (JAK2^R/+); rec, recombined allele (P1 + P2); and wt, wild type allele (P1 + P5).