Genetics and Health

‘Out of Africa’ - 3 studies trace human global migration

by Elaine on February 24th, 2008

Papers published in Nature and Science this week support the previously held theory that humans originated in East Africa, migrating outward until they reached all parts of the globe. But the genetic work from these studies brings a new level of precision to human migration studies, with each group finding subtle and intriguing details that shed light on different aspects of human genetic variation and ancestry.

Study 1 - University of Michigan:This study was based on the analysis of more than 500,000 SNPs and nearly 400 copy number variants — sections of DNA that are repeated or duplicated in the genome — for 485 individuals. These samples, representing individuals from 29 different populations around the world, were obtained as part of the Human Genome Diversity Project.

The results suggest East Africans are the most genetically diverse, while Native American genomes exhibit the lowest genetic diversity. Middle Eastern, Asian, and European populations, on the other hand, fall somewhere in between.  By following this decline in diversity, the Michigan team was able to retrace global human migration patterns. Consistent with previous archaeological date, language studies, and smaller genetic studies of mitochondrial DNA or autosomal or sex chromosomes, the research suggests humans originated in Africa, migrating first to the Middle East, then to Europe, Asia, the Pacific Islands, and — eventually — the Americas.

Study 2 - Cornell University: This study used comparative genomics to analyze 39,440 autosomal SNPs in 10,150 sequences from 15 African-Americans and 20 European-Americans.  Using the PolyPhen computer algorithm, they also assessed how many of the nucleic acid changes in each population were likely to produce amino acid changes that were “possibly” or “probably” damaging.

The researchers observed that the overall genetic diversity was higher in those of African descent, they found that those of European descent had more genetic variations that were predicted to be damaging. The authors attribute this to differences in population age and suggest European populations may have undergone a more recent population bottleneck — a decrease in population that leads to the selection of certain genetic traits — than their African ancestors.

Study 3 - Stanford Human Genome Center: This large study assessed 642,690 SNPs from 938 individuals from 51 populations and measured the genetic variation at each of the loci  and provided valuable information into human genetic variation both on a global scale as well as within relatively small geographic areas.

Specifically, the study found evidence for decreasing haplotype heterozygosity in populations as they moved further and further away from Addis Ababa, Ethiopia.  The study also found genetic evidence for differences in ancestry within populations. For instance, some individuals from the Middle East, such as Palestinians, Druze, and Bedouins, had ancestors from the Middle East as well as Europe and parts of South and Central Asia.

The results of these studies, while intriguing from a human ancestry perspective, may also provide insights into interpreting the genetics of some diseases, since they provide a framework for understanding genetic variation.

Elaine Warburton  www.geneticsandhealth.com
 

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POSTED IN: Chromosome abnormalities, DNA, DNA profiling, Evolution, Genealogy and DNA, General Genetics and Health, Genes, Genetic Ingenuity, Genetic Testing, Genetic adaptations, Genetics of Disease, Human Genome, Population genetics, SNPs, chromosomes