26 February 2008

Human population genetics: the first of a new wave of research

Scientists from the University of Michigan and the US National Institute of Aging conducted the most extensive and detailed study of human genetic variations, the results of which provide new information about the early stages of human migration from the African continent and the distribution of human populations around the globe.

The authors characterized more than half a billion DNA markers of the human genome and analyzed their occurrence in 29 populations living on five continents.

According to one of the leaders of the work, Dr. Noah Rosenberg, this study is the first of a new wave of genome-wide scans of population genetic variations with an extremely high degree of resolution. He emphasizes that new techniques providing simultaneous analysis of hundreds of thousands of genetic markers provide results sufficient to draw conclusions about interactions between human populations and prehistoric human migrations with a much higher degree of reliability than was previously possible.

The data obtained in the framework of this study are a hundred times more detailed than the results of earlier studies in population genetics on a global scale. Based on the data obtained, the authors formulated the following conclusions:

– a newly discovered type of genetic variation – variations in the number of copies of DNA fragments (copy-number variant, CNV) – is an important addition to the arsenal used by population geneticists, which should speed up the work on identifying genes associated with diseases. The authors identified 507 previously unknown copy variations, representing large fragments of DNA (up to a million sequentially arranged "letters" of the genetic code) present in the genomes of some individuals and absent from others. Such an abnormal increase in the number of copies of genes or their loss can lead to the development of various diseases;

– in some cases, the origin of a person can be traced to a separate population living in a certain geographical region. While earlier studies allowed us to obtain approximate information about the geographical origin of a person, new results indicate that the accuracy with which it is possible to determine the place of residence of an individual's ancestors increases with the improvement of methods;

– human genetic diversity decreases as the distance to the cradle of humanity – Africa increases. People of African descent are genetically more heterogeneous than the population of the Middle East, which, in turn, is more heterogeneous than Asians and Europeans. The most similar genomes are characteristic of Native Americans. As a result, the search for disease–associated genes in the genomes of Indians requires a minimum number of genetic markers, and in the genomes of Africans - the maximum.

The results of the work are placed in open databases. The authors hope that they will help scientists in studying the variability of genomes and genetic associations with various diseases.

In total, the DNA of 485 people was analyzed in the framework of the work, in whose genomes three types of genetic variations were searched: single nucleotide polymorphisms or "snips" (he Eng. single-nucleotide polymorphisms or SNP), haplotypes and variations in the copyness of DNA fragments.

If the human genome is presented in the form of a book with three billion letters inscribed in it, snips will correspond to changes in the spelling of individual letters, haplotypes – words, and variations in copyness – the absence or repetition of entire pages.

The patterns revealed as a result of the work confirm the theory of the African origin of people who subsequently settled the territory of the Middle East, somewhat later Europe and Asia, the islands of the Pacific Ocean and, last of all, North and South America.

They also confirm the idea of a consistent manifestation of the "founder effect". This means that people began migrating east from East Africa about 100,000 years ago, while each subsequent wave of migrants carried with them only a part of the genetic variations belonging to the group from which it separated. Thus, the migration process has significantly reduced the level of genomic diversity.

Experts believe that the next level of work of such a plan will be genome sequencing. According to one of the leading authors of the work, Dr. Mattias Jakobsson, a complete decoding of the genomes of 500 people will provide information about almost all important genetic variants.

Evgeniya Ryabtseva,
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of ScienceDaily


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