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Disappointing Results

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  • Disappointing Results

    Completed my Y-DNA test quite a few years back and had no direct matches - Certainly nobody with the same surname.

    I did however have a match at a GD of 2, and the Tip report was encouraging.

    40% chance of common ancestor in 2 generations
    60% chance in 3 generations
    71% in 4 generations
    82% in 5 generations
    88% in 6 generations

    So, we are very likely related I thought. I checked with the individual if he had any links to my family name or to London where my father is from and discovered amongst users from the entire globe, this man was born within 2 miles of my father, about 8 years later. His father and grandfather lived within the same small area of North London as my family going back several generations. But his Grandfather had moved into the area from the west country, so I could pretty much narrow down the window for any likely link between the families.

    And yet, after a bit of effort, we have conducted a Family Finder test so narrow down the relationship and found there is no link at all.

    I'm quite surprised. The Y-DNA is perhaps nowhere near the accuracy I was expecting. Looking back beyond three generations, it is unlikely the two families would have any common ancestor in any predictable time. Is this often the case for Y-DNA? This is just a total coincidence that we are a close match and the fact they lived locally is a coincidence too?

  • #2
    What is the predicted haplogroup and how many STRs have been tested?

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    • #3
      Originally posted by Special25 View Post
      Completed my Y-DNA test quite a few years back and had no direct matches - Certainly nobody with the same surname.
      How many markers did you test? How many markers did your match test?

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      • #4
        Sorry, should have said. We both tested 67 markers.

        GD of 1 at 37 markers
        GD of 2 at 67

        The predicted haplogroup is M253. Not sure I know enough to be fully understanding of the significance of Haplogroups. We both have this same predicted group

        I know from a separate test on 23andMe, my father was initially listed as I1 and then this was amended to P109 which I believe is all part of the same thing. I don’t know if I can automatically assume that that is now my final SNP

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        • #5
          A few thoughts:

          1. I'm not sure it is impossible for you to be half first cousins with the other gentlemen. "On average," half first cousins (eg, same grandfather, different grandmother) share 6.25% of their autosomal DNA, but I think it might be possible from them to share none. The close Y-DNA match and proximity are intriguing.

          2. I think TiP percentages may very well overstate the probabilities. FTDNA does not disclose how TiP is calculated, so it may not consider the possibility of back mutations, which would change the probabilities significantly.

          3. STR testing is all just probabilities. Y-DNA SNP testing is much more definitive.

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          • #6
            I-P109 is downstream of I-M253. Basically the first person to carry the P109 SNP descended from the first person to carry M253.

            Does this person have the same surname as you? Perhaps your common ancestor predates the time period that autosomal testing can detect?

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            • #7
              No, we do not share the same surname

              I had thought the most likely option was a Non Paternity Event in the previous generation or maybe one more further back, but even as a half cousin I would expect this to show on an Autosomal Test

              I have put the results on Gedmatch and carried out a close one to one chromosome browser to see if there is anything at a close in level, but there doesn't look to be anything.

              What would the SNP test actually tell us? That we are both in fact P109, but will it say anything more?

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