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Thread: Are two matches at the EXACT same position likely to be IBC?

  1. #1
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    Are two matches at the EXACT same position likely to be IBC?

    I have two 7.3 cM matches at the exact same position on chromosome X: One mesures 558 SNPs while the other mesures 463 SNPs, but they both start and end at the EXACT same positions. The first one is a male and the second is a female, with whom I also share 10.7 cM (313 SNPs) autosomal.

    Should I just disregard this X matches? Or can I safely assume that these people belong to my mother's side of the family?

    BTW, I am a male.

    Thanks
    Last edited by Ibericus; 01-01-2020 at 01:42 PM.

  2. #2
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    My father got on MyHeritage Scandinavian matches with 7 or 8 CM segments, that I consider to be older than 900 years ago, because the presence of my paternal lineage is attested in South Europe since the 12th century (Anglo-Norman colony in Tortosa), and since then no more admixture with North European populations has occurred.

    But the number of shared SNP's was something like 2000 per 7 CM segment, which counterbalanced the shortness of the DNA segment.

    On GedMatch my father got a match with an archaic DNA from Sweden: 2500 or 3000 years ago, 7 CM but only 200 shared SNP.

    So at first glance I would say that under 1000 shared SNP and with a 7 CM segment you are no more sure to be within the historical timeframe (maybe the anthropological timeframe) or it could be a false positive.

    I hope to find one day a serious statistical study about the IBD shared segment size and shared SNP number distribution according to the TMRCA.

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     msmarjoribanks (01-02-2020)

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