Frequency of V617F homozygosity in patients with ET. (A) Frequencies of wild-type, V617F-heterozygous, and V617F-homozygous BFU-Es in the peripheral blood of 17 ET patients were determined using PCR and BsaXI digestion. The number of colonies genotyped from each patient is at the top of each column. (B) BsaXI digestion of JAK2 exon 14 and SCL intron 1 was used to genotype DNA from peripheral blood BFU-Es cultured from 2 ET patients following transformation to PV (patients 37 and 38). Lanes 1-10 show individual colonies; lane 11, undigested granulocyte DNA from a V617F-negative control; lane 12, BsaXI-digested granulocyte DNA from a V617F-negative control; and lane 13, water.