Web address:
http://www.sciencedaily.com/releases/2011/05/
110524153536.htm
Population Genetics Reveals Shared Ancestries: DNA Links Modern Europeans,
Middle Easterners to Sub-Saharan Africans
A recent study casts new light on the intermingling and migration of European,
Middle Eastern and African and populations since ancient times. (Credit: © Alx
/ Fotolia)
ScienceDaily (May 24, 2011) More than just a tool for predicting health,
modern genetics is upending long-held assumptions about who we are. A new study
by Harvard researchers casts new light on the intermingling and migration of
European, Middle Eastern and African and populations since ancient times.
In a paper titled "The History of African Gene Flow into Southern Europeans,
Levantines and Jews," published in PLoS Genetics, HMS Associate Professor of
Genetics David Reich and his colleagues investigated the proportion of
sub-Saharan African ancestry present in various populations in West Eurasia,
defined as the geographic area spanning modern Europe and the Middle East.
While previous studies have established that such shared ancestry exists, they
have not indicated to what degree or how far back the mixing of populations can
be traced.
Analyzing publicly available genetic data from 40 populations comprising North
Africans, Middle Easterners and Central Asians were doctoral student Priya
Moorjani and Alkes Price, an assistant professor in the Program in Molecular
and Genetic Epidemiology within the Department of Epidemiology at the Harvard
School of Public Health.
Moorjani traced genetic ancestry using a method called rolloff. This platform,
developed in the Reich lab, compares the size and composition of stretches of
DNA between two human populations as a means of estimating when they mixed. The
smaller and more broken up the DNA segments, the older the date of mixture.
Moorjani used the technique to examine the genomes of modern West Eurasian
populations to find signatures of Sub-Saharan African ancestry. She did this by
looking for chromosomal segments in West Eurasian DNA that closely matched
those of Sub-Saharan Africans. By plotting the distribution of these segments
and estimating their rate of genetic decay, Reich's lab was able to determine
the proportion of African genetic ancestry still present, and to infer
approximately when the West Eurasian and Sub-Saharan African populations mixed.
"The genetic decay happens very slowly," Moorjani explained, "so today,
thousands of years later, there is enough evidence for us to estimate the date
of population mixture."
While the researchers detected no African genetic signatures in Northern
European populations, they found a distinct presence of African ancestry in
Southern European, Middle Eastern and Jewish populations. Modern southern
European groups can attribute about 1 to 3 percent of their genetic signature
to African ancestry, with the intermingling of populations dating back 55
generations, on average -- that is, to roughly 1,600 years ago. Middle Eastern
groups have inherited about 4 to 15 percent, with the mixing of populations
dating back roughly 32 generations. A diverse array of Jewish populations can
date their Sub-Saharan African ancestry back roughly 72 generations, on
average, accounting for 3 to 5 percent of their genetic makeup today.
According to Reich, these findings address a long-standing debate over African
multicultural influences in Europe. The dates of population mixtures are
consistent with documented historical events. For example, the mixing of
African and southern European populations coincides with events during the
Roman Empire and Arab migrations that followed. The older-mixture dates among
African and Jewish populations are consistent with events in biblical times,
such as the Jewish diaspora that occurred in 8th to 6th century BC.
"Our study doesn't prove that the African ancestry is associated with
migrations associated with events in the Bible documented by archeologists,"
Reich says, "but it's interesting to speculate."
Reich was surprised to see any level of shared ancestry between the Ashkenazi
and non-Ashkenazi Jewish groups. "I've never been convinced they were actually
related to each other," Reich says, but he now concludes that his lab's
findings have significant cultural and genetic implications. "Population
boundaries that many people think are impermeable are, in fact, not that way."
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Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by Harvard Medical School. The original article
was written by Joanna Logue.
Journal Reference:
1. Priya Moorjani, Nick Patterson, Joel N. Hirschhorn, Alon Keinan, Li Hao,
Gil Atzmon, Edward Burns, Harry Ostrer, Alkes L. Price, David Reich. The
History of African Gene Flow into Southern Europeans, Levantines, and Jews.
PLoS Genetics, 2011; 7 (4): e1001373 DOI: 10.1371/journal.pgen.1001373
Need to cite this story in your essay, paper, or report? Use one of the
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Harvard Medical School (2011, May 24). Population genetics reveals shared
ancestries: DNA links modern Europeans, Middle Easterners to Sub-Saharan
Africans. ScienceDaily. Retrieved May 25, 2011, from
http://www.sciencedaily.com /releases/2011/05/110524153536.htm
Note: If no author is given, the source is cited instead.
Disclaimer: This article is not intended to provide medical advice, diagnosis
or treatment. Views expressed here do not necessarily reflect those of
ScienceDaily or its staff.
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