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Big-Y no matches but found members who share terminal SNP

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  • Big-Y no matches but found members who share terminal SNP

    So we got our Big-Y results recently, no matches, however joined a group project and I can see that two other FTDNA users share the same terminal SNP, R-Z16540. One traces back to the same country as our ancestor, France, and the other to Germany but with many surname matches to the area of France that used to be Germany, and which is the same region as the first haplogroup match (Grand Est). Neither are surname matches and don't appear on Y matching. On Y matching we have no great matches at a high level.

    I'm not sure what to do next. Is there a way to see if they've tested for the Big-Y? Is it possible to share the same terminal SNP but not be related at all? Is this worth investigating somehow?

    Thanks for any advice as I try to figure out how to navigate this Big-Y data!

  • #2
    In that situation, I would look at the block tree and see if you can get a feeling for how remote your MRCA is.

    Private variants are the the SNPs that FTDNA has identified for you, but aren't shared by anybody else. In theory, you should be able to multiply these by some estimate of the typical span of years or generations between SNP formation, subtract the result from some estimate of typical donor birth year, and arrive at a crude estimate of MRCA.

    In my experience, there's a huge variety in actual mutation rates, further complicated by the fact that not everybody under the block you are comparing has tested to the same resolution, etc., but that initial estimate is at least a starting place. Actual experience can vary wildly, but for starters I'd use something like a 67 year span between SNPs.

    If there's a lot of variety in the number of private variants reported by the various people under the SNP block you're analyzing, you might want to use an average.

    So as a hypothetical example, if, let's say, you're looking to guess at the MRCA birth year for everybody under SNP block X, and their private variants average out to be something like 15, the calculation might look like this:

    Est. avg. donor birth year 1950 A.D.
    Avg. # private variants 15
    Est. avg. mutation rate 67
    Less: Est. TMRCA -1,005
    Est. MRCA birth year 945 A.D.


    Like I said, it's a crude method, but it's a start towards putting your matches in historical context. It's a jumping off point from which you can examine the history of the places where the EKA of these donors lived, and form hypotheses about how they could plausibly connect. If some of the donors have really solid, long pedigrees, you can get some surprising insights.

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    • #3
      Wow, thank you for that Benowicz. I had to read it three times to get my head around it. I checked the block tree and the average for our terminal SNP R-Z16540 is 35 private variants. It says we have 41 private variants. So trying to understand what you're explaining, our common ancestors would all be in year X B.C.?? I can think of some variables I'm trying to answer in my head right now...

      If those two members with the same terminal SNP had the Big-Y would we certainly be a match?
      If they got the Big-Y perhaps some of those private variants would also be shared?
      The vast vast majority in the group we're in are from places like Ireland, England, and Scotland, but I actually found members also from France/Germany who share a terminal SNP that seems rare-ish, that seems significant to me, but if it dates back to the B.C. era is it actually significant?
      The SNP Block shows at the bottom 2 from France, 2 from Germany, 1 from USA and 8 unknown. If they are in the same terminal SNP why do they not show up as matches?



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      • #4
        Originally posted by Brasset View Post
        Wow, thank you for that Benowicz. I had to read it three times to get my head around it. I checked the block tree and the average for our terminal SNP R-Z16540 is 35 private variants. It says we have 41 private variants. So trying to understand what you're explaining, our common ancestors would all be in year X B.C.??
        That sounds right. More sophisticated statistical methods could define the range of possible TMRCA more specifically--and that range is usually pretty wide, in the hundreds if not thousands of years--but it sounds like the single most likely possibility is maybe around 400 B.C.

        Originally posted by Brasset View Post
        If those two members with the same terminal SNP had the Big-Y would we certainly be a match? . . . If they are in the same terminal SNP why do they not show up as matches?
        Not necessarily. I forget FTDNA's criteria for registering matches on Big-Y, but I think it has to do with a certain minimum threshold % of shared variants. Problem is, some of those variants are garbage, and the ratio is effected by things like achieved coverage percentage which are almost completely arbitrary (i.e., resolution of the test each donor has taken, the quality of their sample, and sometimes even their place in the testing queue). People who share a MRCA within say the last 500 years are almost certain to register as matches on Big-Y, I think, but beyond that it's a dice roll. Unlikely for terminal SNPs with a very remote TMRCA. My cousin has two registered matches who don't even share his terminal SNP. They share an SNP that isn't too much further back than the terminal SNP, but it really doesn't provide any additional useful information. Dice roll.

        You can probably gather useful information on people that don't register as matches by Google searching for their terminal SNPs--assuming they're members of a public project with published data.


        Originally posted by Brasset View Post
        If they got the Big-Y perhaps some of those private variants would also be shared?
        If they tested at a lower resolution, say the Big-Y 500, and upgraded to 700, they might test positive for one or two of YOUR currently private SNPs. But the fact that you have tested 700 suggests that none of THEIR currently private SNPs would suddenly become shared upon an upgrade--I mean, you've got the maximum resolution positive, so they would have already registered as shared.

        But sometimes--not often, but sometimes, due to issues like a poor scan coverage--examination of the chromosome browser detail on your 'Results' tab will show that FTDNA made a mistake, that you actually are positive for someone else's *currently identified* private variants, or an SNP in another, nearby branch of the block tree. That doesn't happen very often, so it's usually not worth a massive effort to find out, but maybe something to think about if you get super bored during lockdown. FTDNA will be happy to look at the information for any possible mistakes you alert them to, and correct any actual mistakes. Again, doesn't happen too often, so don't expect to find anything.


        Originally posted by Brasset View Post
        The vast vast majority in the group we're in are from places like Ireland, England, and Scotland, but I actually found members also from France/Germany who share a terminal SNP that seems rare-ish, that seems significant to me, but if it dates back to the B.C. era is it actually significant?
        The SNP Block shows at the bottom 2 from France, 2 from Germany, 1 from USA and 8 unknown. If they are in the same terminal SNP why do they not show up as matches?
        Your terminal SNP sounds like it has a very remote MRCA, so that geographic variety is probably real. By seeing how sub-groups of them connect to one another you might be able to form some very speculative hypotheses about how they got there--it would be cool if one of two of them had reliable pedigrees going back to the Middle Ages or so. But yeah, with that extremely large time frame to deal with, the hypotheses are going to be extremely speculative. Maybe future people being added to the tree will clarify the situation, but if so it's likely to be an incredibly slow process.

        Plus, you have to consider the basis on which those donors are assigning a country of origin. My best guess is that, due to FTNDA's marketing considerations, a good number of them will be Americans of colonial ancestry who don't have a firm basis in contemporary documentation for their European origins. Their surnames are probably all from Indo-European languages, so it's incredibly easy to get the wrong idea where they come from just based on the current form of the name, or its resemblance to another, well-documented surname. May not be too reliable. You can only really know if you look at their pedigrees and the quality of the supporting data, which they may or may not be willing to share. My sense is that there is a strong tendency to over-attribute to certain countries, just because of what we (mistakenly) believe about U.S. history.

        For starters, I would probably focus on the Germans and the French, and see whether they cluster in a tightly defined geographic subregion whose history you can explore. Chances are there isn't much known about what was going on in 400 B.C., but maybe the region was associated with some Roman-era tribes that left one or two mentions in the chronicles.

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        • #5
          My Big Y 700 test is now 17 weeks in processing with no results. How large is the backlog and how many samples per week are being completed and released. This wait is excessive

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          • #6
            As of today, the page in the FTDNA Learning Center for how long results take shows Big Y processing to be 12-14 weeks (typically 6-10 weeks). There is always the possibility that your DNA sample was:
            • insufficient to be processed, or failed Quality Control more than once
            • is currently being reprocessed due to failing Quality Control the first time
            as well as taking longer simply due to many tests being processed.

            DNA testing for genealogy is a test of patience (as all things for genealogy seem to be), but you can contact FTDNA Customer Support by using the link at the top right of the forum pages, to see if they will check on your kit's progress.

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