Selective advantage for mutated cells during erythropoiesis and granulopoiesis. The JAK2 617V>F/total JAK2 ratio in immature and mature hematopoietic cells from 5 ET and 13 PV patients was determined by real-time quantitative allele-specific PCR. Histograms represent the JAK2 617V>F/total JAK2 ratios in immature cells (bone marrow CD34⁺CD38⁻ cells), committed progenitor cells (CD34⁺CD38⁺), and mature cells (erythroblasts, granulocytes). □, Mean JAK2 617V>F/total JAK2 ratios from 5 ET patients; ▨, mean JAK2 617V>F/total JAK2 ratios from 4 PV patients with a heterozygous profile (PV h); ■, mean JAK2 617V>F/total JAK2 ratios from 9 PV patients with a homozygous profile PV H. Error bars indicate SD. The P values were determined using the paired Student t test.