Microsatellite analysis to identify regions of homozygosity. The V617F genotype of the patients is indicated as either homozygous normal (WT/WT; patients 1-30) or homozygous mutant (M/M; patients 31-57). Microsatellite markers on chromosome 9p are shown in order from the most telomeric (D9S1779) to the most centromeric (D9S171) and are scored as homozygous (black), heterozygous (white), or not done (gray). Based on published rates of heterozygosity,²³  significant tracts of chromosome 9p homozygosity (LOH/UPD) were scored if 4 consecutive markers above or below JAK2 were homozygous.