Models for the development of V617F^- AML from a V617F⁺ MPD. (A) Three possible models are shown, in which V617F^- AML could develop from (1) a V617F⁺ cell that subsequently reverts to V617F^-; (2) a cell that had some other initiating mutation prior to JAK2; or (3) a normal stem cell. (B) Microsatellite analysis on peripheral-blood granulocytes and T cells from the PV phase of disease (taken in 1992) and blasts from leukemic transformation (2004) for 2 markers on chromosome 9p either side of JAK2 from patient PV2.