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Bushmen neighbours are genetically continents apart

22 February 2010
Appeared in BioNews 546

Comparing the genomes of Archbishop Desmond Tutu and !Gubi, a Khoisan elder from the Kalahari, reveals that, although they are geographical neighbours, their genomes are as different from each other as they are from European or Asian individuals. These findings, published in the journal Nature, reflect the extent of human genetic diversity on the African continent.

Archibishop Tutu and !Gubi are the first southern Africans to join just eleven people worldwide who have had their genomes fully sequenced and made publicly available for research. Until now, only one other African genome - a Yoruban individual from Nigeria - had been sequenced.

Genetic and genomic research has concentrated on European and Asian populations until recently. But it is thought that modern humans originated in Africa approximately 200,000 years ago and a small population migrated to Asia and Europe 70,000 years ago, bringing with them only a subset of human genetic diversity.

Researchers, lead by Dr Stephan Schuster from Pennsylvania State University, identified Archbishop Tutu and !Gubi as representatives of two southern African groups that could shed light on the human genome's diversity. Archbishop Tutu was selected because of his Tswana and Nguni ancestry, the two largest Bantu groups in southern Africa, who make up approximately 80 per cent of southern Africans. !Gubi is the elder leader of a group of Khoisan Bushmen, who are believed to have lived as hunter-gatherers in the Kalahari region for tens of thousands of years and are the oldest known lineage of modern human.

Their genomes were compared to the reference human genome, and the genomes of European, Asian, and Nigerian Yoruban individuals. The researchers identified more than one million new DNA variants within the Bantu and Bushmen genomes that were not shared with the European, Asian or Yoruban genomes, nor with each other.

'On average, there are more genetic differences between any two [Khoisan] in our study than between a European and an Asian', said Professor Webb Miller from Pennsylvania State University and a co-lead author on the study.

The protein-coding regions of three other Bushmen elders were also sequenced. The majority of genetic variants identified in the Bushmen genome were new variants that had accumulated since its lineage diverged from other human populations, and did not represent ancestral genetic variants.

The researchers found the Bushmen genome had several genetic variants that may be associated with a hunter-gatherer lifestyle, such as the ability to store water in body tissues, as well as variants involved in susceptibility to malaria and obesity.

Dr Schuster and colleagues hope that the genomes may help to identify differences in genetic susceptibility to diseases and response to drugs. They may also contribute to the development of more effective anti-retroviral drugs to treat HIV (human immunodeficiency virus), as some southern Africans respond poorly to existing drugs. Archbishop Tutu added:

'Genetic information is important for pharmaceutical companies in preparation of drugs and it is for that reason among others that I agreed to participate in this research'.

SOURCES & REFERENCES
Africa yields two full human genomes
Nature |  17 February 2010
Complete Khoisan and Bantu genomes from southern Africa
Nature |  17 February 2010
Genomes of Desmond Tutu & Bushmen Show Africa’s Huge Genetic Diversity
Discover Magazine |  18 February 2010
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