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Understanding First Cousin Testing

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  • Understanding First Cousin Testing

    A - female - father A
    B - female - father B
    C - male - mother C

    Father A, father B and mother C are brothers and sisters. A, B, C, should be first cousins. A and C test 1st cousins (x-match). B to A test 4th to remote cousins (x-match.) B to C test 5th to remote cousins (no x-match). All related, but female B is testing distant cousin to A and C. I would like to understand if this is possible with autosomal DNA testing? Three first cousins not testing to be first cousins? Of course, other answers could be testing went bad, or B's father/mother is not who she thought or ??? My question is, should I be looking for other answers because autosomal DNA first cousin testing is 100% accurate?

  • #2
    Unless C's test results were actually mixed up, and C got someone else's results (a very remote possibility), C is either adopted or babies were accidentally switched in the hospital at C's birth.

    You can contact FTDNA about the possibility of a mix-up. You could also test C again setting up a completely new account, so that you get a new sample collection kit and a chance to get different results. If the results are different and you get cousin level amounts of DNA, FTDNA will reimburse you for the second test.

    See shared DNA amounts here https://thegeneticgenealogist.com/20...ed-cm-project/

    There is no way true 1st cousins can show up as 4th to remote or 5th to remote on a DNA test. They share lots of DNA and the test will not fail to pick it up.

    You have a very delicate situation to handle, I believe.

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    • #3
      Originally posted by MoberlyDrake View Post
      Unless C's test results were actually mixed up, and C got someone else's results (a very remote possibility), C is either adopted or babies were accidentally switched in the hospital at C's birth.
      I believe you mean the problem would be with B, and it might not be with B necessarily (but it could) but the other possibility is that father B was adopted but maybe more likely B's father isn't who she thinks. Since we don't know the situation either could be possible.

      Originally posted by TheTruth View Post
      A - female - father A
      B - female - father B
      C - male - mother C

      Father A, father B and mother C are brothers and sisters. A, B, C, should be first cousins. A and C test 1st cousins (x-match). B to A test 4th to remote cousins (x-match.) B to C test 5th to remote cousins (no x-match). All related, but female B is testing distant cousin to A and C. I would like to understand if this is possible with autosomal DNA testing? Three first cousins not testing to be first cousins? Of course, other answers could be testing went bad, or B's father/mother is not who she thought or ??? My question is, should I be looking for other answers because autosomal DNA first cousin testing is 100% accurate?
      How much cM's are shared between B and A, and how much cM's are shared between B and C? Not that it matters a whole lot as first cousins shouldn't come in as distant cousins on a DNA test. Double check everything, if you ordered multiple kits for various family members are you sure you sent the correct kits to the correct people? I know some people order many kits during a sale testing close and more distant relatives so make sure a problem might not have occurred with something like that.

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      • #4
        You are right. I did not read carefully enough. Not awake yet.

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        • #5
          First Cousins?

          A little background- A is my mother- I was trying to find her biological father A. B was a potential first cousin (fathers were brothers) and she offered to take DNA test! I have a kit sent to B, she tested and we obtain the results. I order a kit for my mother and she test. I waited for B’s results, to make sure she was in the data base for my mother to be compared to. Results for my mother A – B is 4th to remote (73 shared cM, longest block 12). But, to my surprise, there is a first cousin match to my mother - C! I contact C and his mother was A and B’s sister! And C shows up in B’s matches, but as a 5th to remote (82 cM, longest block 8) A, B and C are all matches within each other’s DNA, just not as first cousins, as I expected. They do share DNA with each other. I don’t see how adoption could fit in, since there is a common bloodline, as remote as it is. B did send in her kit during the flood in Houston, so could it be bad testing? Is my assumption correct in that adoption can be ruled out, if they all are in each other’s matches, no matter how remote, there is a common bloodline?
          I am just being extra careful before I say anything to B. She offered to help us with DNA testing and we find out she isn’t who she thinks she is! Not a story I wish to tell!
          Thank you for your help!

          Comment


          • #6
            Originally posted by TheTruth View Post
            I don’t see how adoption could fit in, since there is a common bloodline, as remote as it is. B did send in her kit during the flood in Houston, so could it be bad testing? Is my assumption correct in that adoption can be ruled out, if they all are in each other’s matches, no matter how remote, there is a common bloodline?
            I am just being extra careful before I say anything to B. She offered to help us with DNA testing and we find out she isn’t who she thinks she is! Not a story I wish to tell!
            Thank you for your help!
            The shared DNA isn't that much to be very significant (and no the flood in Houston had no effect on FTDNA's results). The bottom line is that B is not a first cousin to the others. I don't think you can rule anything out but you would know the family situation better than anyone here. Were the 3 siblings raised under the same roof by the same parents? Did they come from a small town?

            The two scenarios are either:

            1.)Father B was adopted (or less likely switched at birth). In this scenario there is not enough DNA shared for Father B's daughter to be even a 1/2 1st cousin which would mean he was adopted. As far as the shared DNA sometimes extended family members do adopt a child or if they were from a small town or from the same area and just happened to be distantly related that might explain.

            2.) Father B was a sibling but B is not his daughter.

            My guess is scenario 2 is more likely and B just happens to share a common ancestor with A and C through either B's mother's or unknown father's side. Again if they are all from a small town or from the same area that could explain. Really there is no way to tell from the results which scenario is the correct one, to figure it out you would have to test additional people. You found the information you were seeking so I don't think in your case additional testing would be necessary but there is a messy situation in dealing with B, not sure of what advice to give there.

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