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"Double Cousins": DNA Ramifications?

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  • "Double Cousins": DNA Ramifications?

    I have long been aware of this relationship, but until the advent of genetic genealogy, I had never given it much thought. Now, I wonder if these relationships might be profitably used to tease apart other relationships, rule out others, etc.

    In this example, my maternal grandfather's first cousin married my maternal grandmother's brother. This led to a situation where my great aunt by marriage was also my first cousin twice removed by blood.

    I have been in contact with a descendant of this couple and the relationship(s) work out like this:

    Going down my maternal grandfather's line from our common ancestor, we are third cousins. Going down my maternal grandmother's line, this individual and I are second cousins.

    So, first, what is the degree of kinship and how much DNA would be shared between this individual and me?

    Can this relationship be exploited for the purposes of matching, triangulation,etc?

  • #2
    You are more likely to share around 260 cM, than 212.50 cm on average 2nd cousins share.

    It might be more difficult to discern which family the matches are coming from.

    W. (Mr.)