Figure 2: Individual VKORC1(1639 G→A) genotypes, overlaid on the genetic distance dendrogram for a Puerto Rican population (where sectors 1, 2 and 3 correspond to Amerindian, Caucasian, and West African heritage, respectively). Green color represents G/G genotype; whereas, blue and red colors are for the G/A and A/A genotypes, respectively. P-values were calculated by a chi-squared test comparing observed allele frequencies with expected frequencies given the overall allelic ratios. The VKORC1 SNP 1639 G→A is in high linkage disequilibrium with haplotype A, which has been associated with a signifi cant decrease in the warfarin dose per allele. Reprinted from Clin Chimica Acta 2010; 411:1306-11 [16], with permission of Elsevier Ltd.