Ploidy analysis of cultured MKs. BM from control and JAK2V617F animals was cultured with different concentrations of TPO (1 and 50 ng/mL), and ploidy measured in the cells positive for CD41 (a surface marker for MKs) at days 3 and 5 of culture. No difference was observed using 50 ng/mL of TPO (not shown), but the ploidy profile at day 3 with 1 ng/mL of TPO (upper graph) showed a significant increase in high ploidy MKs (≥8N) when compared with control in the CD41⁺ population. This difference was lost by day 5 of culture (lower graph). Error bars represent SD for 3 different MK cultures.