Hello, The following was posted on the ISOGG (International Society of Genetic Genealogist) web. I think it is appropiate to post on this forum. I am posting in its entirety. John R. Carpenter La Mesa, CA Date: Mon, 31 Oct 2005 00:26:58 -0500 From: John <[email protected]> Subject: Y-DNA Testing - What can do and what it can't do With all the discussion about Triangulation Method vs. Phylip diagrams and Fluxus diagrams I think many of us are losing sight of what Y-DNA testing is all about and what it can and cannot do for us. Testing DNA is a very exact science and extremely reliable and accurate. Test results themselves are almost always correct. But what do the test results mean? By themselves they mean very little. It is only by comparing them to other test results that they take on any meaning for genealogists. The only way to derive information by comparing test results is to make assumptions and use statistical analysis. Mutation rates are a key component of computing TMRCA but no one really knows what the mutation rates are and there are several different estimates of the average mutation rate. There are also different ways of counting mutations and each produces it's own TMRCA. Statistic analysis by it's very nature can only provide a range of probabilities. All these factors introduces a great deal of uncertainty into the analysis of DNA test results. So where does that leave us? Y-DNA testing is just another tool to be used by genealogical researchers. A tool to help us support or refute existing paper trails, break through brick walls, and hopefully connect and steer researchers in the right direction. Y-DNA testing cannot prove a relationship though it can certainly provide compelling evidence to support one and can certainly disprove a relationship. Y-DNA testing cannot establish a most recent common ancestor but it may provide some information on when this common ancestor might have existed. As project administrators we recruit participants, have their DNA tested, try to interpret their test results, and try to connect the participants to other participants. In some cases this may be quite straight forward as when two participants believe they share a known common ancestor or when it is believed that two ancestral lines are related and the test results confirm or refute this belief. In other cases it is far more difficult as when participants with no known relationship match closely on the DNA test results. As project administrators it is only natural that we what to "prove" a connection, find the common ancestor, or at least compute the ancestral haplotype of the common ancestor. So we turn to all the tools of Y-DNA testing: triangulation, Phylip diagrams, and Fluxus diagrams. But in reality what do these really get us; a theoretically haplotype or a hypothetical diagram which may or may not depict the truth. Does any of this really bring us any closer helping the participant realize his real goal of furthering his genealogical tree? Without a well documented paper trail the best DNA testing can do is help point participants in the right direction in continuing their research. Participants who closely match on their results can combine their efforts, compare notes, and work together to further their research. The answers, in the end, will only be found through conventional research. While it might be of great satisfaction for the 30 participants in my Group 1 to know they most likely descend from the "original" Blair of Blair back about 1200, this knowledge is of little value to the participant who's paper trail ends in Laurel Co., KY in 1800. Scottish DNA - Better than Life Insurance John ----- John A. Blair Goffstown NH http://blairgenealogy.com mailto:[email protected] BLAIR DNA Project Coordinator