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Ancestry says not a match even with a 16cM segment

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  • Ancestry says not a match even with a 16cM segment

    A good match has appeared at Gedmatch with some of my relatives. They tested at Ancestry. From the mutual matches she has with some cousins I can tell which branch of the family the match is from. But Ancestry isn't recognising her as a match with a male relative of mine.

    They do match at Gedmatch - on Chr 10 they share this segment: 19015198 - 34079354 (16.8669 cM)

    Could this an example of Ancestry "timbering out" matches on popular segments to "help" us?

    I don't think it's a DNA quality issue, as his no call rate is low.

    Her kit: No-calls = 1176 = 0.26198480220816 percent.
    His kit: No-calls = 286 = 0.063713991013208 percent.
    Last edited by ltd-jean-pull; 17 March 2018, 02:38 PM.

  • #2
    You have to determine whether it is a legitimate match or an IBP pileup match.

    At FTDNA I have 8 people that match me for the same 19 cM segment on CHR 8.

    5 of them are at GEDmatch and match me for 19 to 20 cM on CHR 8. 3 of them tested at Ancestry and none of them match me there.

    All 8 of these people are IBP to me and part of one of my pileups.

    What I find interesting is that some of these 8 are related to each other but not to the rest of the 8.

    What is nasty about IBP is that matches triangulate perfectly and that is perfectly useless.

    Ancestry's Timber is an algorithm and is not and cannot be 100% correct in what it does in eliminating matches.

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    • #3
      I'd say it's genuine because at Gedmatch the only other people who match the pair of them on this segment are known close relatives. It's not like some segments which is shared by a couple of dozen people.

      It's a shame Ancestry isn't picking the match because there could be genuine matches who match on that segment that are being missed. If the other person hadn't transferred to Gedmatch we'd still not be aware of this match.

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      • #4
        Originally posted by jimbirk View Post
        You have to determine whether it is a legitimate match or an IBP pileup match.
        There is no sound theoretical basis for IBP. IBP is just a feeble attempt to explain away the pileups. Though it is hard to believe, there is a common ancestor with pileups, and he (yes HE) is not that far back.

        Jack

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