Dartmouth Medical School professor Jason Moore and the rest of an international research team led by Sarah Tishkoff of University of Pennsylvania recently determined that Africans are descended from 14 ancestral populations. The finding was published last month in Science Express.
Image of diversified Africa. Source: http://home.vicnet.net.au/~ebtisama/africa_logo.jpg
Around 200 thousand years ago, modern humans first emerged in Africa and have continuously existed in Africa longer than in any other geographic region, maintaining high levels of genetic diversity. Despite the importance of African population genetics, the pattern of genome-wide genetic diversity across geographically and ethnically diverse African populations is mostly uncharacterized.
“The primary goal is to identify and characterize genetic risk factors for various common human diseases including arterial thrombosis and essential hypertension. Our working hypothesis is that the best predictors of disease susceptibility will come from complex interactions among multiple genetic and environmental factors. The study provides the first comprehensive analysis of the genetic structure and history of Africans and African Americans,” said Moore.
The study revealed tremendous genetic diversity across Africa. It provided great insight into the complex evolutionary history of Africans and African Americans, laying the groundwork for future studies that could lead to important medical advances in Africa and a better understanding of human origins in Africa.
The researchers studied genetic variation among 121 African populations, 4 African American populations and 60 non-African populations for patterns of variation. DNA from volunteers was compared in order to identify various genetic markers throughout the genome, which are sources of variation in individuals, specifically at the 1327 nuclear microsatellite (simple sequence repeat) and the insertion/deletion markers.
The study showed that Africans originated from fourteen ancestral population clusters that correlate with ethnicity and shared cultural and/or linguistic elements. Further, the data revealed high levels of mixed ancestry in most populations, reflecting historic migration events across the continent.
The researchers also observed shared ancestry among geographically diverse hunter-gatherer populations, including pygmies and Khoesan-speakers (known for their click consonants). The ancestry of African Americans is found to be predominantly from Niger-Kordofanian (71%), European (13%), and other African (around 8%) populations.
“In 10 years it will be routine to sequence the entire three billion nucleotides of the genome thus providing all the genetic information for each subject in the study. We will be focusing our efforts over the next several years on preparing our analytical approaches for the mountains of DNA sequence data that will be available on all our African subjects. This data in combination with accurate measures of environmental exposure and analytical approaches that embrace the complexity of the problem is likely to significantly advance our understanding of the genetic basis of common human diseases,” said Moore.