An example of three-way admixture from the HapMap and HGDP samples.

The first three eigenvectors are shown for pooled data of the HapMap populations CEU, CHB, MEX, and YRI and the HGDP population Pima. Samples from MEX were found to be distributed around the inclined triangular plane formed by the clusters of CEU, Pima, and YRI, and most of them were inside the triangle. CEU, Pima, and YRI served as the proxy parental populations of the MEX population. CHB was included to introduce an additional dimension of variation, so that the three-way admixture-related populations formed an inclined triangle.