February 14, 2014
New Interactive Map Reveals Human History Of Genetic Mixing
Lawrence LeBlond for redOrbit.com - Your Universe Online
A multi-institutional team of researchers this week published in the journal Science a study identifying, dating and characterizing the genetic mixing between populations around the world. Along with the study, the team released an interactive map detailing the histories of this genetic mixing.
Researchers from Max Planck Institute for Evolutionary Anthropology, Oxford University and University College London developed sophisticated statistical methods to analyze the DNA of nearly 1500 people from 95 different populations around the world and from over the past four millennia. These populations hailed from Europe, Africa, Asia and South and Central America.
“DNA really has the power to tell stories and uncover details of humanity's past,” said co-senior study author Dr Simon Myers, of Oxford University's Department of Statistics and Wellcome Trust Centre for Human Genetics.
“Because our approach uses only genetic data, it provides information independent from other sources. Many of our genetic observations match historical events, and we also see evidence of previously unrecorded genetic mixing. For example, the DNA of the Tu people in modern China suggests that in around 1200CE, Europeans similar to modern Greeks mixed with an otherwise Chinese-like population. Plausibly, the source of this European-like DNA might be merchants travelling the nearby Silk Road,” explained Dr Myers in a statement.
Dubbed “Globetrotter,” this powerful technique provides a good in-depth look at the past. For Instance, the method provided invaluable insight into the genetic legacy of the Mongol Empire. Historically, it is believed that the Hazara people of Pakistan are partially descended from Mongol warriors; the study found clear evidence to back up this belief, discovering that Mongol DNA had in fact entered the Pakistani population during the Mongol Empire. As well, six other neighboring populations showed similar evidence of genetic mixing with the Mongols during this period.
“What amazes me most is simply how well our technique works,” said study lead author Dr Garrett Hellenthal, of the UCL Genetics Institute. “Although individual mutations carry only weak signals about where a person is from, by adding information across the whole genome we can reconstruct these mixing events. Sometimes individuals sampled from nearby regions can have surprisingly different sources of mixing.”
“For example, we identify distinct events happening at different times among groups sampled within Pakistan, with some inheriting DNA from sub-Saharan Africa, perhaps related to the Arab Slave Trade, others from East Asia, and yet another from ancient Europe. Nearly all our populations show mixing events, so they are very common throughout recent history and often involve people migrating over large distances,” said Dr Hellenthal.
The team also identified “chunks” of DNA shared between individuals from different populations, based on the genome data taken from all 1490 individuals. They found that those populations that shared more ancestry also shared more of these “chunks.” As well, individual “chunks” gave the team clues about the underlying ancestry along chromosomes.
“Each population has a particular genetic 'palette',” said study co-senior author Dr Daniel Falush, of the Max Planck Institute for Evolutionary Anthropology in Leipzig.
“If you were to paint the genomes of people in modern-day Maya, for example, you would use a mixed palette with colours from Spanish-like, West African and Native American DNA. This mix dates back to around 1670CE, consistent with historical accounts describing Spanish and West African people entering the Americas around that time. Though we can't directly sample DNA from the groups that mixed in the past, we can capture much of the DNA of these original groups as persisting, within a mixed palette of modern-day groups. This is a very exciting development,” Dr Falush explained in a statement.
While the new interactive map provides a fresh look at the historical events of genetic mixing, the team feels there is a greater understanding to be taken from the study. They think the new research may have important implications for how DNA impacts health and disease in different populations.
“Understanding well the genetic similarities and differences between human populations is key for public health,” said Dr Myers.
“Some populations are more at risk of certain diseases than others, and drug efficacy is also known to vary significantly. Rare genetic mutations are particularly likely to show strong differences between populations, and understanding their role in our health is an area of intense current research efforts.”
“We hope in future to include even more detailed sequencing, to spot these rare mutations and better understand their global spread. Our method should be even more powerful when applied to these future data sets, providing rich opportunities for future work,” concluded Dr Myers.
Image Below: An interactive map of human genetic mixing. Credit: The chromosome painting collective