January 10, 2017
The Search for our Ancestry (XXXII)
The DNA Testing Community
As more people participate in genealogical DNA testing, more potential relationships can be found. The fact that there are several venues may work at cross purposes to that goal, because you may have your DNA tested by one, while a long-lost cousin may have hers tested at another. In my case, one venue initially failed to extract enough ‘genetic material’ from a sample, while another had no problem doing so. One venue may offer comparison of health and medical-oriented genome characteristics, another might not. AncestryDNA doesn’t offer ‘chromosome mapping’ graphics, others do. One venue may be more understandable than another, or less expensive.
There are ways for users of diverse DNA testing venues to compare their results to those of subscribers to other venues. For example, in many cases, ‘raw genealogical data’ may be downloaded by a subscriber of 23andMe or AncestryDNA, and uploaded to FTdna for a cost that is less than FTdna’s basic testing cost. The genomes from the other venues can then be compared to those of FTdna subscribers, Ftdna’s ‘Surname Projects’ can be joined, etc.
Another similar venue is the free site www.gedmatch.com (GEDmatch) which accepts raw data from other venues. Users provide their contact information, and give permission for their e-mail addresses to be posted. This is an advantage over 23andMe, for example, since correspondence can be made directly via e-mail, rather than by anonymous correspondence through the vendor. However, some participants who freely give their e-mail address still don’t respond to e-mails!
GEDmatch has more-detailed graphics (chromosome mapping) of DNA segment matches than does 23andMe. Like 23andMe, it allows you to set the ‘significant’ length of segments to be considered (7 centiMorgans (cM) is generally considered as significant), but through color-coding, it also shows shorter shared segments. GEDmatch allows ‘one-to-one’ and ‘one-to-many’ comparisons. The former are similar to comparisons on 23andMe, but with more detail in the graphs. The ‘one-to-many’ comparisons list all users who have a match of at least 7 cM, and include the length and number of matching segments, an e-mail address, the % of matching DNA, and the estimated number of generations to a common ancestor.
Interestingly, some ‘relatives’ whose DNA I compared to mine on both 23andMe and GEDmatch show minor differences in results: a matching segment being 22 cM in one and 25 cM in the other; or a segment match in three chromosomes rather than in just two. Since the ‘raw data’ in both cases is identical, this seems to reflect differences in the software algorithms used by each venue. So some of the error in the analyses is not just ‘lab error’ in extracting genetic material from my saliva, but ‘computer error’ in the sense that two programs analyzed the same data and produced slightly different results.
One aspect of DNA testing the subscriber-provided ‘family tree’. Most venues allow participants to enter their own family trees into the system: 23andMe has a routine wherein you start with your own name and add ancestors on-line, until the tree is as complete as you want it; GEDmatch allows uploading of a family tree data file created by an off-line program; AncestryDNA links to your tree on Ancestry.com.
I had hestitated to upload my tree to a DNA testing site, for fear of ‘circular logic’ that would use my own research to ‘prove’ a DNA relationship. I have found, though, that having DNA results ‘attached’ to a family tree helps ‘DNA relatives’ to determine which ones, of possibly hundreds of others, they should attempt to contact to expand their knowledge of family. This is not a recommendation, as users must decide for themselves which venue is best for them. In my case, AncestryDNA serves me best. I am able to ‘attach’ my DNA results to my on-line family trree and also view the trees of my ‘DNA matches’. AncestryDNA does not provide ‘chromosome mapping’, but that is easily achieved by uploading my data to the free GEDmatch, which allows many other valuable comparisons.
Coniglio is the author of the book The Lady of the Wheel, inspired by his Sicilian research. Order the paperback or the Kindle version at http://bit.ly/SicilianStory