Interplay among JAK2V617F copy number, clonal composition, and disease phenotype. Clonal composition in ET and PV patients can be varied and complex and can have a direct impact on disease phenotype. Analysis of clonally derived erythroid progenitors demonstrated that the clonal composition of ET patients consists of a population of JAK2V617F-heterozygous cells with either no or a small and unexpanded population of JAK2V617F-homozygous cells. In contrast, the clonal composition of PV patients can consist of either near to complete dominance of the entire cell compartment with JAK2V617F-heterozygous cells, or a population of JAK2V617F-heterozygous cells with an expanded population of JAK2V617F-homozygous cells.