Announcement

Collapse
No announcement yet.

Using Test Results to Explore Possible Consanguinity

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Using Test Results to Explore Possible Consanguinity

    Can autosomal DNA results help determine if a person's paternal grandparents were half-siblings (assuming that the grandchild is the one tested)?

    If so, what would one need to look for among the test results (or matches) to determine if there is a possibility that one's grandparents were closely related?

  • #2
    The ideal solution is to do the familyfinder test on the grandchild's father. Then you would transfer the raw data to www.gedmatch.com and run the utility called Are Your Parents Related.

    If you cannot do that, I cannot think of a simple way of just using the grandchild's results. A average grandchild would have 8 greatgrandparents each sending down roughly 12.5 percent DNA. The grandchild you describe would have 7 greatgrandparents with one of the lines sending down roughly 25 percent of the DNA. I suppose you would have to conduct a targeted set of tests of close relatives to see if you could try and prove that relatives of that one line are sharing more DNA than you would suspect. It would be hard to prove without multiple example comparisons.

    Comment


    • #3
      Thanks for your response. This is as I expected. Unfortunately, the "grandchild" is an adult in her 60s and her father and grandparents are of course all deceased.

      In this possible scenario, the half-siblings share the same mother ... but their respective father's were also closely related. The "grandchild" shares an inordinate number of "extremely high" matches with relatives of the mother of the half-siblings. The shared cMs for some of these matches also seem quite a bit higher than the average for the known degree of relatedness.

      The "grandchild" also shares an extremely high number of matches with both of the respective father's of the half-siblings. In fact, the paternal matches for the "grandchild" up through the "4th to 6th cousin level" are virtually all connectible in some way to the mother of the half-siblings, and her two husbands.

      The one set of relatives completely absent from the grandchild's matches are those of her legal paternal grandfather (the one on paper). In fact, two known 2nd cousins from the paternal grandfather's family who have tested do not share detectable cMs above a 5cM strand.

      Altogether, all of this may suggest nothing, but it's got me thinking about that strange old family story ...

      Comment


      • #4
        Originally posted by Giusvalla View Post
        In fact, two known 2nd cousins from the paternal grandfather's family who have tested do not share detectable cMs above a 5cM strand.
        If you are saying these are paper-trail second cousins to you (or whoever the focal person is - not clear about that,either), and do not share detectable cMs with you (or ...) - then this is almost certainly significant, and is a strong indication that paper-trail is not a real bio-trail.

        Comment


        • #5
          Originally posted by loobster View Post
          If you are saying these are paper-trail second cousins to you (or whoever the focal person is - not clear about that,either), and do not share detectable cMs with you (or ...) - then this is almost certainly significant, and is a strong indication that paper-trail is not a real bio-trail.
          The focal person is my mother, and these are her "paper-trail" 2nd cousins. These 2nd cousins are maternal grandchildren of her grandfather's sister. They didn't show up as matches on Ancestry, which of course surprised us, but I was able to upload their respective results to gedmatch. Gedmatch indicates that the 2nd cousins do not match my mother nor her sister at the range of 7 cM or above.

          After my mother and her sister tested, we were at once able to identify matches that belonged to their mother's side. No questions there.

          Mom's father's side made a lot of sense at first too, we found lots and lots of matches to their paternal grandmother. But we found no matches to their paternal grandfather's family lines (all are pre-colonial families that arrived in the U.S. before 1640).

          However, we do have several close matches to the family of mom's paternal grandmother's stepfather (these are 2nd cousin range matches). Strange!

          This really confused us at first, and of course we are reluctant to want to accept that we are not genetically related to who we always thought was mom's grandfather. But, there was a family story about mom's grandmother "going home" before the birth of mom's father, then having to "leave suddenly." Mom's grandfather left the family abruptly around the same time, and his mother moved away from her family and several months later had my grandfather. And she never went home nor spoke with her family after that. When my grandfather reconnected with his mother's family later in life, they alluded to some kind of scandal.

          This is an uncomfortable story. We may never have wondered anything more about it if it wasn't for the DNA testing we did. We now wonder what this all means?

          Comment

          Working...
          X