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Analysis Question for You DNA Buffs

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  • Analysis Question for You DNA Buffs

    Good morning. I have an analysis question.

    I have been contacted by someone who is unknown to me but indicated "closely related-1st cousin" on Ancestry. The other is an adoptee who had interacted with her birth mother's family but has an unknown father. We compared my DNA to her maternal sample on Gedmatch - no match. Thus, her father is either my uncle (deceased) or my father (uninterested). On Gedmatch, total of matching segments > 7cM = 1857.3 cM, and estimated MRCA was 1.5. Could she in fact be my half-sister? I have had samples submitted for my brother and one of my uncle's sons - will this help, or without direct paternal DNA will we ever really know?

    Thanks for your time!

    - khutchinson

  • #2
    Are you a male or a female? If the latter, and you have the same father, you will match on the entire length of the X chromosome.

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    • #3
      I am female. The Gedmatch autosomal comparison tool seems to have left out chromosome #23. I will go back and do more research. Thank you so much for your help!

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      • #4
        Originally posted by khutchinson View Post
        I am female. The Gedmatch autosomal comparison tool seems to have left out chromosome #23. I will go back and do more research. Thank you so much for your help!
        It is a separate utility, X 'one-to-one'.

        Jack

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        • #5
          You are "most likely" half siblings. Other possibilities are:

          Full sibs: but that would yield Base Pairs with Full Match (green bars) in GedMatch. Your numbers are also way low for this; nominal would be ~2700 cM.

          Grandparents: You could likely rule this out by ages; if not the number and sizes of segments could help; half sibs would have half as many but twice as long segments than half-sibs.

          Aunt/Uncle: Again, number and size of segments, and ages, can help out here.

          First Cousin: Your numbers are way high, but possible...

          Common matches can help, as well.

          Bob
          Last edited by hansonrf; 3 October 2015, 09:20 AM. Reason: clarity

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          • #6
            I presumed the uncle you referred to was your father's brother. Did your father have any other siblings or known offspring (male or female) who could test? My concern is that his brother could have the identical X from their mother and that might lead you astray.

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            • #7
              Most likely half siblings.

              If you haven't already, check out the chart here: http://www.isogg.org/wiki/Autosomal_DNA_statistics

              These are averages and actual amounts can vary, but I think you share way too much to be first cousins. Since the situation sounds highly unlikely to be double first cousins and based on ages, you're probably not grandparent/child, that leaves half siblings or aunt/niece.

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              • #8
                It's a Sister!

                Well, we have a matching X-gene. I will ask my aunt (father's sister) if she would test as well. However, we have determined that during the time period this person was conceived in 1959, my father was in the area on leave from the USN. Additionally, my dad matches the general description given by the birth mother (age, etc.), and she looks a LOT like my dad. I guess what they say about sailors is true... I am very excited to have met this person - she and I have some very real similarities, besides physical resemblance. A lot of joy comes with this discovery. Thank you for your help.

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                • #9
                  Originally posted by khutchinson View Post
                  Well, we have a matching X-gene. I will ask my aunt (father's sister) if she would test as well. However, we have determined that during the time period this person was conceived in 1959, my father was in the area on leave from the USN. Additionally, my dad matches the general description given by the birth mother (age, etc.), and she looks a LOT like my dad. I guess what they say about sailors is true... I am very excited to have met this person - she and I have some very real similarities, besides physical resemblance. A lot of joy comes with this discovery. Thank you for your help.
                  It's nice to hear you embracing this, I've heard a lot of stories of people in your situation who are angry to discover it, or in denial, and reject their new found half-sibling.

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                  • #10
                    my second cousin that i know is my second cousin had a 257cm. so that person is way closer than my cousin

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