Visual genotypes of APOE in the core data. Color codes represent the genotypes at each polymorphic site in each individual in the sample: blue for homozygous for the common allele, red for heterozygous, and yellow for homozygous for the rarer allele. (a) Jackson sample, (b) North Karelia sample, and (c) Rochester sample. Individuals homozygous across the locus are marked with an asterisk.