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Old 22nd July 2017, 08:35 AM
Armando Armando is offline
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Join Date: Jun 2009
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Originally Posted by TwiddlingThumbs View Post
If it's a different surname, then a gd at 67 does not mean they match. Lots of false positives with different surnames. FTDNA's gd guidelines re matches only apply to men with the same surname.
There are too many NPEs to be able to state that a 67 marker match with a person that has a different surname isn't a match from a genealogical timeframe. The false positives can only be confidently be weeded out by Y111 and/or BigY testing or a similar NGS or WGS test.
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Old 22nd July 2017, 08:44 AM
Armando Armando is offline
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Join Date: Jun 2009
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Originally Posted by TwiddlingThumbs View Post
Per the following ISOGG article on convergence, a low gd number with someone of a different surname may not indicate any relationship. The lower gd may due to convergence, ie, two unrelated lines having STR results that converged due to a series of mutations that closed the STR marker gap between the two lines. The likelihood that a low gd may be due to convergence depends on a lot on your haplotype. According to the article, for 5-10% of surname groups, up to 90% of their matches might be false positives. If you have a close gd with someone of a different surname, it is worth a look, but may not indicate any relationship. https://isogg.org/wiki/Convergence
This is from your convergence link "It is less likely to occur at 67 markers, though a case has been reported of two 67-marker haplotypes with a genetic distance of 6, which were found to be in different R1b subclades"

What they don't say in that sentence, but should, is that a match with a GD of 6 or 7 has a very high probability of not having a common ancestor in the past 500 years which generally most people can't even get past that in their genealogy. They also fail to mention that some 67 marker matches no longer match once the person and the match upgrade to Y111 and that this is due to not having a common ancestor in the past 500 years. Beyond 500-1,000 years then STRs are less reliable than NGS testing estimate how long ago the common ancestor lived.

Last edited by Armando; 22nd July 2017 at 09:22 AM.
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Old 22nd July 2017, 04:40 PM
clintonslayton76 clintonslayton76 is offline
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Join Date: Jun 2014
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In other words....

In simplest terms, if two 67 matches, regardless of surname, each expand their results to 111, they should not diverge from matching if they share a common ancestor within historical genealogical terms. If they continue to show as matches, then it should be investigated as possibly findable with paper genealogy. The genetic distances are guesses, but having 67 matches with the same surname should not mismatch at 111, the mutations are "more recent" but the haplo is not affected. With different surnames, a close match bears further research, but enough mutations to show 6 to 7 gens is probably not worth your time unless there is supplementary evidence to create suspicions.
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