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Old 12th October 2017, 09:45 PM
SurplusGadgets SurplusGadgets is offline
FTDNA Customer
Join Date: Mar 2016
Posts: 12
My experience has been different. The last thing I worry about is a surname when determining a match and grouping in a project. The first criteria (when available) is deep SNP test match; always. Next is STR match. Then we look at the surnames to classify as a variant, deviant or likely "NPE". People join our project either because of a surname match and/or an STR match to someone in our project.

I have one tightly knit group with over 10 surnames. And none are adopted. Just, for whatever reasons, these families decided to change to a mother's family name (more than once) over the last 300 years. They all descend from a common male ancestor after 1600. And they are all the only matches each other have (over 15 matches at y37; all patrilineal related). (We have shown that they were all living near each other in early, colonial Virginia with the families intermarrying.)

I have another group with similar surnames (variations, deviations) where with just a y12 result we can tell they are in the same group with the common ancestor from about 1500 or later. They simply have some very unique (rare) STR marker values in 3 of the y12 test suite markers. BigY has proven this out with the members.

Yet I have a few other groups that have 20+ y67 Matches that are not only not the same surname but known not to be the same patrilineal line. Their "real" patrilineal matches appear in the middle of the ordered STR match list. There are a few Haplogroups (DF27 in this case) where it appears this convergence occurs (in abundance). The STR test does not ever predict a very deep Haplogroup. Doing BigY or similar deeper SNP testing shows these testers are either in or not in the same patrilineal line. The ones in my surname study have "identical" matches to each other with BigY. Some of the other y67 STR matches who have done deeper SNP testing show they are down a different branch of P312 than DF27 (e.g. L20).

So, from experience, I do not think you should be making any statement of relatedness (or lack thereof) purely on given surnames. And not make any statement of likely convergence until you have deep SNP testing compared that shows they are different. Calculating and using GD and TiP without deep SNP testing is just guesswork before understanding more fully.

With all this said, in my experience, if they match STRs and also have the similar (variant, deviant) surname, then likely they match deep SNPs and a patrilineal relationship can be found if not known already.

I would finally add that the GD and TiP calculation is varied among these different groups as well. Some, with MRCA's of less than 200 years, have GD's of 3 or 4 at 67 markers. Others, with MRCA's over 300 years back, have GD's of 1 or 2 at 111 markers. So calculation of genetic distance and TiP from STR marker comparisons is still not a very exact science. Independent of Surnames matching but always only looked at if deep SNPs match. This large variance is even when taking into account different weighting factors for highly versus slowly varying markers. There is more going on than is maybe understood at this time. (I suspect related to the locations of markers in certain DNA areas prone to more major, connected changes.)

Last edited by SurplusGadgets; 12th October 2017 at 09:55 PM. Reason: Clarify some wording
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