Admixture dynamics in Hispanics: a shift in the nuclear genetic ancestry of a South American population isolate

Abstract

Although it is well established that Hispanics generally have a mixed Native American, African, and European ancestry, the dynamics of admixture at the foundation of Hispanic populations is heterogeneous and poorly documented. Genetic analyses are potentially very informative for probing the early demographic history of these populations. Here we evaluate the genetic structure and admixture dynamics of a province in northwest Colombia (Antioquia), which prior analyses indicate was founded mostly by Spanish men and native women. We examined surname, Y chromosome, and mtDNA diversity in a geographically structured sample of the region and obtained admixture estimates with highly informative autosomal and X chromosome markers. We found evidence of reduced surname diversity and support for the introduction of several common surnames by single founders, consistent with the isolation of Antioquia after the colonial period. Y chromosome and mtDNA data indicate little population substructure among founder Antioquian municipalities. Interestingly, despite a nearly complete Native American mtDNA background, Antioquia has a markedly predominant European ancestry at the autosomal and X chromosome level, which suggests that, after foundation, continuing admixture with Spanish men (but not with native women) increased the European nuclear ancestry of Antioquia. This scenario is consistent with historical information and with results from population genetics theory.

Fig. 1.

Y microsatellite haplotypes for five common surnames in Oriente. Each row represents a different individual. The rightmost column indicates surnames. The other six columns represent Y-microsatellite loci (the prefix DYS has been omitted). Alleles and surnames have been color-coded with each color representing a different allele or surname.

Fig. 2.

The expected change in European ancestry over time when the rate of gene flow per generation m = 0.083 and 0.074 for autosomal (dotted line) and X-linked (solid line) loci, respectively, obtained using recursion Eq. 2 in Materials and Methods.