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Triallelic diagram of the ABO blood group allelic frequencies for human populations. Each point represents a population; the perpendicular distances from the point to the sides represent the allelic frequencies, as indicated in the small triangle. Populations 1 to 3 are African, 4 to 7 are Native American, 8 to 13 are Asian, 14 to 15 are Australian aborigine, and 16 to 20 are European. Dashed lines enclose arbitrary classes with similar gene frequencies; these groupings do not correspond to “racial” classes. (After A. Jacquard, Structures génétiques des populations. Copyright © 1970 by Masson et Cie.)