[LINK] "MPeople from Mexico show stunning amount of genetic diversity"

[rfmcdonald]

National Geographic's Karen Weintraub wrote about a new study in Science, described here by Lizzie Wade, about the genetics of Mexico's indigenous populations. It turns out that Mexico's populations are very diverse. This has significant implications for, among other things, medical treatments and diagnoses, besides revealing interesting things about Mexico's pre-Columbian history.

Mexico contains 65 different indigenous ethnic groups, 20 of which are represented in the study, says Andrés Moreno-Estrada, a population geneticist at Stanford University in Palo Alto, California, and the study’s lead author. Working with Carlos Bustamante, another Stanford population geneticist, the team sampled the genomes of indigenous populations all over Mexico, from the northern desert of Sonora to the jungles of Chiapas in the south. Over centuries of living so far apart—and often in isolation because of mountain ranges, vast deserts, or other geographic barriers—these populations developed genetic differences from one another, Bustamante explains. Many of these variants are what he calls “globally rare but locally common.” That is, a genetic variant that’s widespread in one ethnic group, like the Maya, may hardly ever show up in people of different ancestry, like people of European descent. If you study the genomes of only the Europeans, you’d never catch the Maya variant. And that’s a big problem for people with Maya ancestry if that variant increases their risk of disease or changes the way they react to different kinds of medication. “All politics is local, right? What we’re starting to find is that lots of genetics is local, too,” Bustamante says.

When the team analyzed the genomes of 511 indigenous individuals from all over Mexico, they found a striking amount of genetic diversity. The most divergent indigenous groups in Mexico are as different from each other as Europeans are from East Asians, they report online today in Science. This diversity maps onto the geography of Mexico itself. The farther away ethnic groups live from each other, the more different their genomes turn out to be.

But most people in Mexico or of Mexican descent these days are not indigenous but rather mestizo, meaning they have a mixture of indigenous, European, and African ancestry. Do their genomes also vary by what region of Mexico they come from, or has all that local variation been smoothed out by centuries of different groups meeting, mixing, and having babies?

To answer that question, the team collaborated with Mexico’s National Institute of Genomic Medicine, which has been collecting genetic data from mestizos for many years. Somewhat surprisingly, they found that mestizos in a given part of Mexico tended to have the same “rare” genetic variants as their indigenous neighbors. The mestizo genomes “track so well with the indigenous groups that we could use the genetic diversity in mestizos to make inferences about [their native] ancestors,” Pasaniuc says. Strong genetic markers of Maya ancestry, for example, show up in the genomes of modern people living in the Yucatán Peninsula and the northern part of Mexico’s Gulf Coast in the modern state of Veracruz, which likely reflects a pre-Columbian Maya trade or migration route. “It gives us a historical understanding of what these populations have been up to,” says Christopher Gignoux, a postdoc in Bustamante’s group at Stanford.