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Any advice in approaching group matches?

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  • Any advice in approaching group matches?

    My mother has a large shared fragment on chromosome 16 with two other individuals (~48 cM). Based on our trees, the common ancestor is not recent. Approximately 45 people on Family Finder (and more in Gedmatch) match within this fragment to these three people. My phased DNA on Gedmatch shows the same fragment and matches (when those individuals have uploaded there).

    As you would expect, not all of these people match one another; the people on the short arm match one another as the people on the long arm do, with the individuals spanning the centromere often matching both.

    We have yet to find a common ancestor although all of us have holes in our trees. Most of us have predominantly southern US roots but there are some whose ancestry lies to the north. We could very well overlap in PA or VA. A recent addition to the group appears to have entirely Norwegian heritage.

    What is the best way to approach this? I think of us as a unified group. With three people distantly related having the same fragment, I envision a common ancestor with this fragment. It seems like the odds would be rather long for this to have been assembled three times at random. Others are more inclined to pursue their subgroups, which I think is also useful.

    Does anyone have any experience that they could share?

    Thanks for any insight,

    Pat

  • #2
    One thing I might suggest: Use admixture calculators on GEDmatch to see which ethnic groups that particular shared segment seems to include -- using the chromsosome painting features.

    About the Norwegian match: My father gets a huge number of Norwegian matches (one grandmother was Norwegian). Yet, he seems to be getting a minority of British matches which I had assumed were, in fact, connected to his French ancestry (his other grandmother was French-Canadian). I believe one recent match was solidly connected to Yorkshire. My knowledge of British history is limited, but somewhere I found out that Yorkshire had been invaded and settled not only by Danes but also Norwegians. (British forum readers, pleas comment!) I am now wondering if his British matches are, in fact, related to his Norwegian ancestry (or perhaps his minority Danish genetic ancestry).

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    • #3
      I have ancestors on my father's mother's side who hail from New England where close-knit religious groups stayed close. 'Cousin' marriages create what is called pedigree-collapse or the founder-effect which causes distant cousins [like 6-8th or even 10th] to share much larger than expected segments, and if you look carefully, many small segments.

      The point is you may find multiple common ancestors but a good bit further back.

      Bob

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