JAK2 V617F mutations. Fluorescent dye chemistry sequencing chromatograms showing homozoygous (top) and heterozygous/mixed clonality (middle) guanine to thymine substitution (arrow) in exon 12 of JAK2 in granulocyte genomic DNA from 2 patients with MDS. The predicted protein consequence is substitution of phenyalanine for valine at position 617 of NP_004 963. The bottom chromatogram is the wild-type sequence.