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Thread: Reliability of the X chromosome as IBD, as opposed to IBS

  1. #11
    Administrator
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    1,976
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    Canada
    Ethnicity
    Mixed Euro/Near East
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    Canadian
    Y-DNA
    R1a-YP4516/YP4807*
    mtDNA
    H11a2a3

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    Hm. The only thing I can think of is that perhaps there may be no-calls for the child and homozygous non-matching calls for the mother (especially if they were tested on different platforms).
     

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    Other ancestral Y lines:

    E1b-M81 Ukraine (Ashkenazi)
    E1b-V13 England
    I1-M253 Ireland
    I2-M423 Ukraine
    R1a-L176.1 Scotland
    R1b-L584 Syria/Turkey (Sephardi)
    R1b-L20 Ireland
    R1b-L21 (1)England; (2)Wales?>Connecticut
    R1b-L48 England
    R1b-P312 Scotland
    R1b-FGC32576 Ireland

    Other ancestral mtDNA lines:

    H1b2a Ukraine (Ashkenazi)
    H6a1a3 Ukraine
    K1a9 Belarus (Ashkenazi)
    K1c2 Ireland
    V7a Ukraine

  2. #12
    Registered Users
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    Pittsburgh, PA, USA
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    German-British-Catalan
    Nationality
    (U.S.) American
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    R-L1029
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    H1bg

    Germany Palatinate United Kingdom Catalonia France Ireland Switzerland
    I ended up comparing my sister's and daughter's matches X chromosome matches at FTDNA, which allows a lower matching threshold than 23andMe.

    Sure enough, the segment which shows up for my sister and me but not my sister and my daughter at 23andMe, did show up for my sister and my daughter at FTDNA. All three of the shared segments show up as slightly longer between my sister and my daughter than for my sister and me. Clearly, there is a bit of false matching based on the fact that each of them has a second X chromosome. It's a difference of between 1-2 cM for each segment.

    In addition, FTDNA actually shows a fourth matching segment between my sister and my daughter. This is reportedly 6.6 cM in length, but it cannot be real because I don't have the matching segment. (And my wife and my sister don't match here -- or anywhere -- either.)
    The short explanation of my ancestry is German-British-Catalan, but it actually includes smaller amounts of French, Irish, Swiss, Choctaw and probably Cherokee. My avatar picture is of my father, his father, and his father's father. The baby in the picture is my eldest brother.

    GB

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     AJL (06-13-2017)

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