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Shared matches

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  • Shared matches

    I have two known cousins, one maternal and the other paternal, so I would expect any unknown DNA matches to share a match with one of them. But most of my DNA matches when checking shared matches does not match with either of them. How is that possible? I'm simply looking at 2nd-3rd cousins so not too far out. What am I missing in understanding matching DNA?

  • #2
    Matching is not an exact science. The whole business is operating on some bad assumptions.


    • #3
      bitstone I'm not sure if the below is what you are checking, because it sounds like you are checking the shared matches of your unknown matches, and not the shared matches for your known cousins.

      Are you doing this: go to one of your known cousins in your Family Finder match list, and click on the box to show a checkmark. You can then select "in Common/Not in Common" by clicking the symbol that looks like a person's head and shoulders, at the right (above where it shows "X Match") for that cousin. This will give you a choice for "in Common" or "Not in Common." Choose "In Common," and this will give you the matches in common with you and your cousin. That will be the most direct way of seeing if any of your unknown 2nd-3rd cousin matches are a match to your known cousins.

      You should also make a tree at FTDNA, or upload a GEDCOM file to create a tree, which includes these two known cousins. You can then link them to their places in your tree. This will help to filter your Family Finder matches into maternal and paternal lists.


      • #4
        You absolutely should get the phasing activated from your 1st cousins. But they wont phase all your matches. My mother only phases 40% of my matches. My dad (untested) was a similar Colonial background and he might have phased another 40%. Prior to 2021, phasing both parents at FTDNA resulted in about 65% phasing (IIRC) They updated their algorithms last year so phasing is now a little more complete.

        My point being that first cousins will phase a LOT of your matches but they will also miss a lot. It probably also depends on the actual cousin. I have a first at 23andMe, who I share a significantly below average number of cM and she filters out less than 20% of my matches (Relatives in Common).

        Those matches who dont match either parent are likely false matches. To some extent, those who dont match either maternal or paternal cousin, may also be false matches, bur its hard to completely say that since first cousin phasing is not complete. Also FTDNA does not phase segments below 8.5 cM.

        Phasing is one of the strengths of FTDNA. You can add any known 2nd to 4th cousins for additional phasing. At other sites, its parents only.