NEW YORK (GenomeWeb News) – A study published online today in Science described the marked genetic diversity detected in Mexican populations, providing information that's expected to help in interpreting population histories, disease risk, and more.
An international group led by investigators at Stanford University, the University of California at San Francisco, and Mexico's National Institute of Genomic Medicine (INMEGEN) genotyped more than 500 Native Mexicans from 20 indigenous groups in Mexico and about as many Mexican mestizos — admixed individuals with Native Mexican, European, and African ancestry.
Within the indigenous Mexican populations, the team saw distinct, geographically related genetic clusters that reflected long-term population splits within the country, stretching back hundreds or even thousands of years in some cases. In the admixed individuals, meanwhile, it detected Native Mexican ancestry patterns that largely coincided with the genetics of indigenous populations with roots in nearby regions of the country.
"[T]here's been a tremendous language and cultural diversity across Mexico, with large empires like the Aztec and Maya, as well as small, isolated populations," the study's co-first author Christopher Gignoux said in a statement.
"Not only were we able to measure this diversity across the country, but we identified tremendous genetic diversity, with real disease implications based on where, precisely, your ancestors are from in Mexico," added Gignoux, who was a graduate student in co-corresponding author Esteban González Burchard's UCSF lab when the study began. He is currently a post-doctoral researcher at Stanford.
The Mexican genetics effort stemmed from an interest in understanding genetic patterns outside of populations with European ancestry. Expanding this view of genetic variation within and across human populations has implications for interpreting past human migrations, population relationships, and genetic disease risk.
"Understanding the genetic structure of a population is important for understanding its population history, as well as designing studies of complex biomedical traits, including disease susceptibility," co-senior author Carlos Bustamante, director of Stanford's Center for Computational, Evolutionary and Human Genomics, said in a statement
A few prior studies have started untangling diverse genetic factors that contribute to disease risk in different populations. In a paper published just this week in the Journal of the American Medical Association, for example, researchers from the SIGMA Type 2 Diabetes Consortium reported on a rare variant that's specifically associated with type 2 diabetes in Latino populations.
The current analysis uncovered more fine-scale biological differences within populations from Mexico, including lung capacity differences that coincided with the extent of western or eastern Native Mexican ancestry found in various admixed mestizo populations.
"These results suggest that fine-scale patterns of native ancestry alone could have significant impacts on clinical measurements of lung functions in admixed individuals within Mexico," Bustamante, González Burchard, Gignoux, and co-authors wrote.
The researchers profiled almost a million SNPs apiece in 511 individuals from 20 Native Mexican populations for their study. Together with data on previously characterized West African and European populations and genotyping data on 500 admixed individuals from Mexico and the US, variant profiles in the indigenous individuals' genomes helped them identify genetic clusters corresponding to both geography and ancestry.
The genetic profiles in Native American individuals included in the study tended to cluster along a continuum from northwest Mexico to the southeastern region of the country. In the country's northern region, for example, the team saw ancestral similarities between the Tarahumara, Tepehuano, and Huichol populations.
A southern ancestry component, on the other hand, was more common in Triqui, Zapotec, and Mazatec populations, while populations near the Yucatan peninsula carried a Mayan ancestry component that was less common in other parts of the country.
The researchers saw especially pronounced genetic differences between the Seri population, found on Mexico's northern mainland near the Gulf of California and the Lacandon, a population with Mayan ancestry that resides in a region near Guatemala. The genetic distance between the Seri and Lacandon was on par with that separating populations in Europe and China, they noted.
Within the admixed Mexican populations, the team noted that Native American and European ancestry tended to predominate, with most mestizo individuals carrying 5 percent African ancestry or less.
And while historical colonization by Spanish settlers have left their mark in the European ancestry component of many admixed mestizo individuals, findings from the new analysis suggest that Native American ancestry in modern-day Mexican genomes is largely linked to Native Mexican populations present in different parts of the country prior to colonization.
"[W]e have demonstrated a high degree of fine-scale genomic structure across Mexico, shaped by pre-Columbian population dynamics and affecting the present-day genomes of Mexican mestizos, which is of both anthropological and biomedical relevance," the study's authors concluded.