atDNA About Autosomal Admixture
Findings to date
Autosomal(atDNA) testing is useful for estimating my ancestral admixture at the continental level and where there are people in the world with whom I share DNA. Even so,
atDNA About Autosomal Admixture
Findings to date
Autosomal(atDNA) testing is useful for estimating my ancestral admixture at the continental level and where there are people in the world with whom I share DNA. Even so, I learned companies differ in:
1. Genealogical timeframes used
2. Reference populations sampled
3. Disproportionate ancestry sampling
4. Accuracy of estimating ancestry
5. Delineating populations within a continent.
1. Genealogical ancestral timeframes.
Companies come at ancestry timeframes from different perspectives. For the most part, 23andme and Ancestry atDNA tests are oriented on recent genealogical timeframes, around 500 years ago. The company, 23andMe, analyzes what it refers to as my "Ancestry Composition." This is the percent of my ancestry that comes from each parent DNA based on where their ancestors lived some 500 years ago, as it is reflected by its reference population groups. Along these lines, the Ancestry company provides me with an "Ethnicity Estimate. It compares my DNA to that of people with similar DNA and with extended family histories going back several hundred to over 1,000 years in a particular world region.
In contrast, the XCode.Life company strives to give ancestral information deeper than 500 years. This giving geographical focus to deep ancestry is also the goal of the Family Tree company's ancestry estimations in its atDNA test, "My Origins."
Yet, regarding learning our deep ancestry, geneticist, Razib Khan points out "Europeans, as we understand Europeans today, genetically did not exist 10,000 years ago and South Asians as we understand them did not exist 10,000 years ago." Expressing a consensus among scientists with this view, Ker Than adds in his article in Science on popular DNA testing, "such tests cannot account for recent migrations of peoples from their ancient homelands. Present-day patterns of residence are rarely identical to what existed in the past, and social groups have changed over time, in name and composition."
Commenting on these views, noted geneticist Dr. Adam Rutherford provides even further support in Scientific American, "For deeper family roots, these tests do not really tell you where your ancestors came from. They say where DNA like yours can be found on Earth today."
That said, anthropological geneticist, Dr. Deborah Bolnick suggests, "If a test-taker is just interested in finding out where there are some people in the world that share the same DNA as them, then these tests can certainly tell them that."
2. Reference population ancestry sampling
The estimate of ancestry refers to a type-population in a given geographical region for any single individual. The accuracy of DNA tests for one's distant ancestral past relies on the sampling population used to develop the DNA profile of the ancient people from a geographical region. If the people used to develop the profile are without admixture (pure-bloods from the tested region), the sampling population is representative of the people from that region. In contrast, if the people tested for the profile have an admixed profile, it influences the accuracy of the regional profile.
Moreover, ancestry estimates differ because the sampling reference populations used by each company differ. Each company relies on its proprietary database for DNA reference sampling, and there are no established guidelines for the representation of ancestry.
3. Disproportionate ancestry sampling.
Test populations proportion to global population distribution are disproportionate. People of European ancestry make up less than 25% of the global population. Yet, they represent the majority of the participants in the genetic research of companies mostly based in the United States. As a result, these companies have an extensive Eurocentric database but relatively small and limited Asian reference populations for estimating ancestry. However, as Figure 2 shows, these companies are continuously refining their estimations of ancestry by expanding their ancestry reference population databases and reaching out to reinforce global coverage to include Asian populations.
Three companies serve the people of Asia, which accounts for ~60% of the world's population.
The company, XCode Life, is based in India and claims to cover the 23% of the world's population of South Asia heritage. This area includes the 1.75 billion people of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.
WeGene DNA and Zuyan DNA, based in China serve the 1.6 billion people, 38% of the world's population, who live in East Asia. These are the countries of China, Mongolia, No