While most genomewide association studies completed to date have focused on populations of European ancestry (see Table 1 for examples), we expect that genomewide association scans will be conducted in much more diverse groups of samples. The success of genotype imputation depends critically on the choice of reference population from which densely characterized haplotypes are drawn. For studies of European ancestry samples, it is now clear that the HapMap CEU samples (102-104) usually constitute an appropriate reference panel. Similarly, we expect the HapMap CHB+JPT (102-104) samples will constitute a good reference for imputing genotypes in samples of East Asian ancestry and that the HapMap YRI (102-104) samples will constitute a good reference for imputing genotypes in populations of West African ancestry.
