Re: 65 of 67 DNA match from FTDNA
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In reply to:
Re: 65 of 67 DNA match from FTDNA
Nona Anon 12/17/10
Melissa1
>>The closest person in our Surname that I share ydna with is off by ONE. I have No exact matching person.
The next closest person is off by about 3 or 4 and continues to go up exponentially from there all the way up to 8 mismatches even though we ALL of the exact same surname and HaploType.<<
I assume you meant haplogroup.
This is the problem with comparing living to living. The level of mismatches within a family can be very wide. With a common surname and common haplogroup (especially, R1b), there might overlapping with someone who is not related in the time frame of fixed surnames.
Another problem is that the TMRCA model seems simple on the surface, but there are some subtleties that make them more difficult in practice. It should not be used within documented genealogies.
The key is to compare living to ancestral or ancestral to ancestral. If there is no paper trail, the modal can be tentatively used. It is made up of the most common values on each marker. If there is a good paper trail, researchers should triangulate the progenitor's haplotype. This is found by testing descendants of different sons until there are matches on each marker.
34/37 or better matches to the ancestral are good in the usual genealogy. 33/37 or 32/37 matches are in a gray area and may be due to the MRCA's living further back than the genealogical time frame or simply the randomness of mutations in a documented genealogy. In the latter case, it is best to test other branches to determine the pattern.
To test the credibility of the documentation, use the forward (binomial) calculation. Count the number of generations from the progenitor, not from an internal branch.
Note also that you need to use an infinite alleles count in a genealogical time frame. This means that the count is either 0 or 1, regardless of FTDNA's GD. Note that FTDNA is going to this on all of the multi-copy markers. They use it on DYS464 and YCAII now. I have not seen anything about the single-copy markers, though. However, they are less of a problem.
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Re: 65 of 67 DNA match from FTDNA
Nona Anon 12/25/10