Heterogeneity in genetic admixture across different regions of Argentina

Abstract

The population of Argentina is the result of the intermixing between several groups, including Indigenous American, European and African populations. Despite the commonly held idea that the population of Argentina is of mostly European origin, multiple studies have shown that this process of admixture had an impact in the entire Argentine population. In the present study we characterized the distribution of Indigenous American, European and African ancestry among individuals from different regions of Argentina and evaluated the level of discrepancy between self-reported grandparental origin and genetic ancestry estimates. A set of 99 autosomal ancestry informative markers (AIMs) was genotyped in a sample of 441 Argentine individuals to estimate genetic ancestry. We used non-parametric tests to evaluate statistical significance. The average ancestry for the Argentine sample overall was 65% European (95%CI: 63-68%), 31% Indigenous American (28-33%) and 4% African (3-4%). We observed statistically significant differences in European ancestry across Argentine regions [Buenos Aires province (BA) 76%, 95%CI: 73-79%; Northeast (NEA) 54%, 95%CI: 49-58%; Northwest (NWA) 33%, 95%CI: 21-41%; South 54%, 95%CI: 49-59%; p<0.0001] as well as between the capital and immediate suburbs of Buenos Aires city compared to more distant suburbs [80% (95%CI: 75-86%) versus 68% (95%CI: 58-77%), p = 0.01]. European ancestry among individuals that declared all grandparents born in Europe was 91% (95%CI: 88-94%) compared to 54% (95%CI: 51-57%) among those with no European grandparents (p<0.001). Our results demonstrate the range of variation in genetic ancestry among Argentine individuals from different regions in the country, highlighting the importance of taking this variation into account in genetic association and admixture mapping studies in this population.

Figure 1. Distribution of genetic ancestry among 441 individuals from Argentina by four major regions.

Each individual is represented by a vertical bar on the X-axis. Bars are divided into percent European (blue), Indigenous American (red) and African ancestry (green). BA = Buenos Aires province; NEA = Northeast; NWA = Northwest; South = South. Individuals on the X-axis are sorted based on increasing Indigenous American ancestry. On the lower right corner we include a map of Argentina indicating the location of the samples. For analysis we grouped samples by region: black: BA, pink: South, grey: NWA, orange: NEA. Samples of individuals from the NEA region (orange) were obtained from the hospitals in Buenos Aires.

Figure 2. Box plots of average individual ancestry by four major Argentine regions.

The blue boxes represent the European component, the red boxes the Indigenous American component and the green boxes the African component. BA = Buenos Aires province; NEA = Northeast; NWA = Northwest; South = South.