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Thread: Matching on X but not Autosomal?

  1. #21
    Registered Users
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    Tunisia
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    R1b-M269
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    L2a

    Tunisia
    Thanks!
    Yes they seem to be IBS, I have just looked in depth and the segments are smaller than 5cM.
    My closest oracles:
    1 CEU + Morocco_Jews + Swedish + Sahara_OCC @ 1.618438 DODECAD V3
    1 BedouinA + German_North + Scottish_West + Tunisian @ 1.355784 puntDNAL K12 Modern
    1 Algerian + BedouinA + British + Norwegian_West @ 2.072077 MDLP K23b

    A thread where I explain how the Tunisian sample used by various gedmatch calcs is not representative of Tunisians:
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  2. #22
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    Pittsburgh, PA, USA
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    German-British-Catalan
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    (U.S.) American
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    H1bg

    United Kingdom Germany Bayern Catalonia France Ireland Switzerland
    Quote Originally Posted by kikkk View Post
    Hi!
    I have 4 X matches with American persons all of them women, does that mean we have a common female ancestor?
    Not necessarily. When it comes to determining whether two people have a common ancestor, size definitely matters. On any chromosome -- not just the X -- if a match is small, there's a greater chance that it might be identical more by coincidence than by common descent.

    On the X chromosome, the only real difference is that when you're comparing two men, you have a greater likelihood that the match is "real" (which means, identical by descent and not just by state). But all four of your matches are female, so you can't tell which of their two copies is involved in the match -- of whether even bits of both.

    Knowing that I got my X chromosome from my mother, does that mean that my maternal grandmother is related to those 4 Americans?!
    Since you're male, you do know that your X chromosome came from your mother. But don't automatically presume that it therefore came from her mother. Remember, a woman inherits an X chromosome from both parents. Therefore, an X chromosome she passes on to a child can consist of: a recombination of both of her X chromosomes; an exact copy of her paternal X chromosome; or an exact copy of her maternal chromosome.

    I've seen this in my own family. Out of my five siblings, all three of my sisters inherited an identical X chromosome from our father. However, two of my siblings -- one of my sisters plus one of my two brothers -- also match each other over the entire span of the copy each received from our mother.

    I match both of these siblings on all but 20 cM of my single X chromosome. Based on matches we share with more distant relatives (including a 2nd cousin, and multiple 3rd cousins and half 2nd cousins), it's clear that these two siblings inherited an unrecombined X chromosome traceable to our maternal grandfather.

    So, don't assume that the most recent common ancestor for a match on the X chromosome has to be female. (Even though, yes, if the MRCA is male, you can go one more generation back to his mother.)
    The short explanation of my ancestry is British-German-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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