#genetic admixture

[dr-afsaeed]

Crusaders’ DNA Revealed History of Crusades History can disclose to us a ton about the Crusades, the arrangement of religious wars battled somewhere in the range of 1095 and 1291, in which Christian trespassers endeavored to guarantee the Near East.

[theolduvaigorge]

Neanderthal ancestry drives evolution of lipid catabolism in contemporary Europeans

by Ekaterina E. Khrameeva, Katarzyna Bozek, Liu He, Zheng Yan, Xi Jiang, Yuning Wei, Kun Tang, Mikhail S. Gelfand, Kay Prufer, Janet Kelso, Svante Paabo, Patrick Giavalisco, Michael Lachmann and Philipp Khaitovich

"Although Neanderthals are extinct, fragments of their genomes persist in contemporary humans. Here we show that while the genome-wide frequency of Neanderthal-like sites is approximately constant across all contemporary out-of-Africa populations, genes involved in lipid catabolism contain more than threefold excess of such sites in contemporary humans of European descent. Evolutionally, these genes show significant association with signatures of recent positive selection in the contemporary European, but not Asian or African populations. Functionally, the excess of Neanderthal-like sites in lipid catabolism genes can be linked with a greater divergence of lipid concentrations and enzyme expression levels within this pathway, seen in contemporary Europeans, but not in the other populations. We conclude that sequence variants that evolved in Neanderthals may have given a selective advantage to anatomically modern humans that settled in the same geographical areas" (read more/open access).

(Open access source: Nature Communications 5:3584, 2014; doi: 10.1038/ncomms4584)

[theolduvaigorge]

Frequently asked questions about “A Genetic Atlas of Human Admixture History” 

by G. Hellenthal, G.B.J. Busby, G. Band, J.F. Wilson, C. Capelli, D. Falush and S. Myers

What is your work about and how is it new? 

"Many researchers have studied human DNA and its history, and this has revealed how humans have spread around the globe. This spreading out produces distinct populations, and small genetic differences between separated populations arise (although most variation is still shared among groups).  When groups come back together – for example due to migrations or invasions - and have children, this is called genetic admixture, and leaves a characteristic signature in DNA. 

 Our work uses DNA from many people around the world to identify these mixture events, and find out first, who the groups were that mixed – often to the level of individual countries – and second, when the mixture occurred. Other researchers have developed important tools to look at one or other these questions but our method is the first to do both simultaneously – allowing us to more fully describe events. By using “chromosome painting”, it also offers better power and precision than previously available. We are able to consider complex histories (e.g. several waves of mixing) and have analysed 95 groups across the globe, producing an “atlas” of mixing dates, places and mixing populations. 

What does your study imply about human ancestry? 

Most human populations are a product of mixture of genetically distinct groups that intermixed within the last 4,000 years. 

Mixture events are often localized in time and space: neighboring populations can sometimes have distinct ancestry and history, especially for recent events. 

Many mixture events involve source populations from very distant locations separated by thousands of miles.

What is genetic admixture? 

Genetic admixture occurs when individuals from two or more genetically distinguishable groups have children together. This might happen when individuals from one part of the world settle into a new geographic region already inhabited by other people, e.g. due to invasions or large-scale migrations.  

What was the aim of your study? 

Our study uses novel statistical methodology seeks to identify and characterize genetic admixture events in the history of the groups in our sample. Results are presented on an interactive webpage at: 

www.admixturemap.paintmychromosomes.com" (read more).

(Source: Welcome Trust Centre for Human Genetics)

[theolduvaigorge]

Genome-wide evidence of Austronesian–Bantu admixture and cultural reversion in a hunter-gatherer group of Madagascar

by Denis Pierron, Harilanto Razafindrazaka, Luca Pagani, François-Xavier Ricaut, Tiago Antao, Mélanie Capredon, Clément Sambo, Chantal Radimilahy, Jean-Aimé Rakotoarisoa, Roger M. Blench, Thierry Letellier, and Toomas Kivisild

"Linguistic and cultural evidence suggest that Madagascar was the final point of two major dispersals of Austronesian- and Bantu-speaking populations. Today, the Mikea are described as the last-known Malagasy population reported to be still practicing a hunter-gatherer lifestyle. It is unclear, however, whether the Mikea descend from a remnant population that existed before the arrival of Austronesian and Bantu agriculturalists or whether it is only their lifestyle that separates them from the other contemporary populations of South Madagascar. To address these questions we have performed a genome-wide analysis of >700,000 SNP markers on 21 Mikea, 24 Vezo, and 24 Temoro individuals, together with 50 individuals from Bajo and Lebbo populations from Indonesia. Our analyses of these data in the context of data available from other Southeast Asian and African populations reveal that all three Malagasy populations are derived from the same admixture event involving Austronesian and Bantu sources. In contrast to the fact that most of the vocabulary of the Malagasy speakers is derived from the Barito group of the Austronesian language family, we observe that only one-third of their genetic ancestry is related to the populations of the Java-Kalimantan-Sulawesi area. Because no additional ancestry components distinctive for the Mikea were found, it is likely that they have adopted their hunter-gatherer way of life through cultural reversion, and selection signals suggest a genetic adaptation to their new lifestyle" (read more/not open access).

(Source: PNAS 111(3):936-941, 2014 ; top image: Wikipedia; bottom image: National Geographic)