Sunday, 19 June 2011

Biogeographical ancestry

Autosomal DNA testing purports either to determine the "genetic percentages" of a person's ancestry from particular continents/regions or to identify the countries and "tribes" of origin on an overall basis. Admixture tests arrive at these percentages by examining SNPs, which are locations on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. Tests' listing geographical places of origin use alleles—individual and family variations on various chromosomes across the genome analyzed with the aid of population databases. As further detailed below, this latter type of test concentrates on standard identity markers, such as the CODIS profile, combined with databases such as OmniPop, ENFSI and proprietary adaptations of published studies.
The admixture tests are designed to tell what percentages a person has of ancestry of Native American, "European", East Asian, and Sub-Saharan African. One company[14] describes these four biogeographic groups as follows:
  • Native American: Populations that migrated from Asia to inhabit North, South and Central America.
  • European: European, Middle Eastern and South Asian populations from the Indian subcontinent, including India, Pakistan and Sri Lanka.
  • East Asian: Japanese, Chinese, Mongolian, Korean, Southeast Asian and Pacific Islander populations, including populations native to the Philippines.
  • African: Populations from Sub-Saharan Africa such as Nigeria and Congo region.
Based on customer feedback, the company in June 2007 introduced a new version of its EURO DNA test, with a more limited range of countries, that promises to provide more meaningful clues to one's European ancestry. Both tests: the four-part ethnicity estimate and EURO DNA test, identify a high number of so-called Ancestry Informative Markers (AIM), whose genetic distance between populations reflects the populations' geographic distance from each other. The location and variation of these AIMs are proprietary to the company and have never been published.
In 2006, another company[15] developed an autosomal DNA ancestry-tracing product that combined the traditional CODIS markers used by law enforcement officers and the judicial system with OmniPop, a population database developed by San Diego detective Brian Burritt. Customers received matches to their profile's frequency of occurrence in world populations, as well as a breakout for European ancestry based on the European Network of Forensic Science Institutes (ENFSI).[16] As a public service, the company has supported the expansion of OmniPop, which currently encompasses over 360 populations, double that of its first release. The ENFSI calculator uses data from 24 European populations (5700 profiles). The two databases must be searched separately, because they are based on two different sets of markers. The company sells its product as the DNA Fingerprint Test. The 16 markers incorporated in its results are: D8S1179, D21S11, D7S820, CSFIPO, D3S1358, THO1, D13S317, D16S539, D2S1338, D19S433, VWA, TPOX, D18S51, D5S818, and FGA.
The theory behind using a forensic profile for ancestry tracing is that the alleles' respective frequency of occurrence develops over generations with equal input of the two parents, since for each location we take one value from our mother and one from our father. It thus serves as a window into a person's total ancestral composition. The configuration of scores reflects inherited changes from all previous generations in all ancestral lines, and can predict an individual's unique probable ethnic matches based on the profile's frequency or rarity in different populations.[17]
To give an idea of the inclusiveness of the latest version of OmniPop, the following are the last populations that have been added:
  • Greek
  • Sikkim (India)
  • Bhutia (India)
  • Italian
  • Argentinian (Misiones)
  • Hungarian (E. Romani)
  • Hungarian (Ashkenazim)
  • Romanian (Szekler)
  • Romanian (Csango)
  • Tibet (Luoba)
As studies from more populations are included, the accuracy of results should improve, leading to a more informative picture of one's ancestry.
Along the same lines, yet another company[18] identifies the indigenous and diaspora populations in which an individual's autosomal STR profile is most common. This test examines autosomal STRs, which are locations on a chromosome where a pattern of two or more nucleotides is repeated and the repetitions are directly adjacent to each other. The populations in which the individual's profile is most common are identified and assigned a likelihood score. The individual's profile is assigned a likelihood of membership in each of thirty-four world regions:[19]

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