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Thread: What does a high percentage of DNA shared in the X chromosome (males) mean?

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    What does a high percentage of DNA shared in the X chromosome (males) mean?

    What does a high percentage of DNA shared in the X chromosome (males) mean? Thx

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    1 out of 1 members found this post helpful.
    Common maternal ancestor

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    Let there be two sisters F1 and F2.
    F1 has a son (say) F1M, while F2 has a daughter (say) F2F.
    F1M and F2F both have a son each, (say) F1MM and F2FM (2nd cousins).
    How could it be that F1MM and F2FM have 50% shared DNA?

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    First of all X chromosome for men is inherited only by mother so F1MM does not share common DNA from at X chromosome with his parental relatives. In general 50% common DNA is too much for second cousins. This amount is shared between siblings.

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    Well, I have a 50% half-match with a 2nd cousin once removed (I am 2nd cousins with his mother).
    See X chromosome comparison below from 23andMe:

    Attachment 10921

    A and B were sisters.
    A had a daughter C and B had a son W (1st cousins)
    C had a son V and W had a daughter D (2nd cousins)
    D had a son U.

    V and U exhibit the above situation (their X chromosomes half-matching for half their length).

    A and B both have the same pair of X chromosomes. Say X1 from their father and X2 from their mother.
    C got X3 from her father and (say) X1 from her mother A.
    Let's assume, for the sake of argument, that W also got X1 through his mother B (50% chance).
    Let's also assume, that C passed X1 to her son V (50% chance). W would pass his single X-chromosome X1 to his daughter D anyway.
    D, having X1 from her father and (say) X4 from her mother, had a 50% chance to pass X1 to her son U.
    This means that was a 1/8 = 12.5% probability that the same X-chromosome would pass to V and U.
    It appears this is what happened here + recombination by A, B, C, and D.

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    Ok yes it is possible to happen. I can't open the link.

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    X 36669149 94634203 42.57 3827 Half
    X 141055608 155092794 27.55 1881 Half

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