Thursday, 13 October 2016

The DNA ancestry craze from The Stream

DNA testing was featured this week in a two-part TV programme on The Stream, an online social-media-oriented TV show hosted by the Al Jazeera media network. The guests on these programmes were: Julie Granka, a population geneticist with AncestryDNA, Joseph Graves, an Evolutionary Biologist at North Carolina A&T State University, and Kevin Jones Giddins, an AncestryDNA user who had found his mother through DNA testing. Questions were submitted via social media and there was a very good and balanced debate on the pros and cons of DNA testing, with a particularly valuable contribution from Professor Joseph Graves. He provided some interesting insights into the methodology used for admixture tests  the reports received from the testing companies that give you the percentages of DNA that you share with different populations. These tests cannot provide the granularity that the companies claim. They can distinguish between populations at the continental level but cannot generally provide meaningful breakdowns at the country level in Europe, Africa or elsewhere. (This might change in future. The new test from Living DNA provides regional breakdowns within the British Isles though we have not yet seen any customer results.)

The programmes mostly focused on results from AncestryDNA. It would have been helpful if they could have shown results from 23andMe and Family Tree DNA as well, and asked scientists from these two companies to contribute to the debate.

There was one matter of concern when one of the presenters, Malika, showed some results that her father had received from a company called African Ancestry back in 2008. You could see from the screenshots that her father had only taken very low-resolution tests (an HVR1 mtDNA test and a 9-marker Y-DNA test) yet the family were told by the company that they were descended from specific tribes in Chad, Cameroon and Ghana. When so few markers are used for a Y-DNA or mtDNA test, the genetic signature could potentially be shared with thousands of people from many different countries, and it is simply not possible to infer an origin in a specific country. Better resolution can be obtained from a full mtDNA sequence test or a comprehensive Y-chromosome sequencing test, but even then it's not generally possible to pinpoint a specific country of origin. An additional problem is that most of the people in the company databases are Americans and Europeans, and there simply aren't enough reference populations from Africa to make such inferences. Unfortunately these Y-DNA and mtDNA results were glossed over in the programme and the limitations of the African Ancestry tests weren't discussed.

However, these are minor quibbles in two otherwise very interesting programmes. It was also good for once to see more of an emphasis on using DNA testing for genealogical matches rather than a mistaken attempt to discover "where you're from". Each programme lasts for just 25 minutes, and they are both well worth watching. Part 1 covers The DNA ancestry craze and Part 2 looked at The science and security of DNA testing. You can click on the videos below to watch the programmes.

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