Schematic representation of technique used to determine JAK2 exon 19 SNP genotype of V617F-positive mutant alleles. (A) Genomic structure of JAK2 gene, showing primers used. (B) Procedure to determine the JAK2 exon 19 SNP genotype of JAK2 V617F mutant–positive alleles using either total cDNA (lefthand side) or individual clones (righthand side).