That modern Homo sapiens emerged out of Africa at some point in time has quite a bit of evidence. But what has remained uncertain was who these adventurous people were. What area of Africa were they from? How many of them were there? And how did they spread out to populate the globe?
Researchers at the University of Michigan and at the National Institute on Aging conducted a detailed study of genetic variation in human populations, which can pinpoint a person’s genetic heritage to a specific population in a geographic region. Results at this level of specificity mean that this information is 100 times more detailed than previous studies.
Data was gathered from 29 populations on five contients, and a total of 500,000 different genetic markers were sequenced. What the data showed was the continual implications of the founder effect, which happens when a small, random subset of a population leaves the main group and reproduces on their own. Because these founder populations are usually so small — sometimes less than 50 people — a mutation that was initially rare in the larger group can become quite frequent in the founder population. So as small groups of humans broke off from the larger population to settle in new areas, the diversity of the group was gradually diminished.
“Now that we have the technology to look at thousands, or even hundreds of thousands, of genetic markers, we can infer human population relationships and ancient migrations at a finer level of resolution than has previously been possible,” said lead co-author Noah Rosenberg, of the University of Michigan’s Life Sciences Institute, in a press release.
From a genetics standpoint, what is especially interesting is the importance of copy number variants (CNV) in DNA. CNVs are long stretches of DNA that can be repeated in different numbers in different people- or deleted entirely. Some genetic diseases, like Fragile X Syndrome, are caused when the copies of a particular DNA sequence get so large that they cause structural abnormalities. With an additional 507 CNVs discovered by Rosenberg’s group, researchers now have more tools to use to screen for potential genetic diseases.
“This data set is so rich. It provides a much more comprehensive, cross-sectional snapshot of the human genome than previous studies,” said Paul Scheet, a post-doctoral researcher in the U-M Department of Biostatistics and one of the lead authors.
Some information and quotes provided by University of Michigan press release.
Jakobsson, M., Scholz, S.W., Scheet, P., Gibbs, J.R., VanLiere, J.M., Fung, H., Szpiech, Z.A., Degnan, J.H., Wang, K., Guerreiro, R., Bras, J.M., Schymick, J.C., Hernandez, D.G., Traynor, B.J., Simon-Sanchez, J., Matarin, M., Britton, A., van de Leemput, J., Rafferty, I., Bucan, M., Cann, H.M., Hardy, J.A., Rosenberg, N.A., Singleton, A.B. (2008). Genotype, haplotype and copy-number variation in worldwide human populations. Nature, 451(7181), 998-1003. DOI: 10.1038/nature06742