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Family Finder Results compared to GEDMatch

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  • Family Finder Results compared to GEDMatch

    I've been searching a long time (since 1975) for my paternal great grandfather. Had my uncle tested (Dad's brother; Dad's been gone 20 years) and also man I suspect is my uncle's 2nd cousin on the paternal side. Family Finder results came back with 2nd - 4th cousin and shared cM of 115. Is shared cM of 115 enough to confirm a 2nd cousin relationship?

    I also ran both results through GEDMatch and that analysis came back with 3.8 generations to MRCA, which seemed to confirm the 2nd cousin relationship.

    Am I letting emotions get the better of me, or have I finally found the link to my great grandfather?

    Thanks for the help.

  • #2
    Confirming a 2nd Cousin Relationship

    dhorner -

    The range given by ISOGG for 2nd cousin matches is roughly 193-338 cM of shared autosomal DNA. However, there have been reports of 100cM or even a bit less for 2nd cousins. So, 115 cM strikes me as theoretically possible, but unlikely. In any event, if I were in your situation (and I have been) I would prefer to triangulate with multiple matches before reaching a conclusion.

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    • #3
      Thanks for the suggestion. I'm in the process of trying to locate a known 2nd cousin to my uncle's match. My suspected great great grand father had 6 sons, 3 of which, by viutue of location and age, could be my great grand father. My uncle's match, i think, eliminated one of those 3 suspected sons because the relationship is not recent enough, even if 2nd cousin turned out to be correct.

      Ill keep plugging away.

      Comment


      • #4
        Here are some numbers for comparison of my sister and me with some documented 2nd and 3rd cousins at 23andMe. Although the algorithms for determining shared DNA are slightly different at FTDNA and 23andMe, they're similar enough that they can be used for comparison.

        2nd cousin & my sister - 297 cM
        2nd cousin & me - 472 cM

        2nd cousin, once removed & my sister - 82 cM
        2nd cousin, once removed & me - 110 cM

        2nd cousin, twice removed & my sister - 66 cM
        2nd cousin, twice removed & me - 77 cM

        2nd cousin, twice removed & my sister - 5 cm
        2nd cousin, twice removed & me - 61 cM

        3rd cousin & my sister - 72 cM
        3rd cousin & me - 107 cM

        3rd cousin, once removed & my sister - 19 cM
        3rd cousin, once removed & me - 42 cM

        All these known cousins are related to my sister and me through my paternal grandfather's lines. You can see that it's probably the case that I have received more of my paternal grandfather's DNA than my sister. She probably received more of my paternal grandmother's DNA than I have.

        Since that's probably the case, her shared DNA with these cousins is closer to the average than my high amount of shared DNA in these relationships. Given that, if I had to guess what the relationship is between your uncle and his match with 115 cM of shared DNA, it seems to be about 2nd cousin, once removed or maybe 3rd cousin. However, it could be a full 2nd cousin relationship with a low amount of shared DNA, although it seems somewhat too low for 2nd cousin.

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        • #5
          Thanks MMaddi.

          I did read that length of shared cM may be more important than the total. Do you have any insight on that? This is the information from GEDMatch for strings > 7cM. Maybe I'm just grasping at straws.


          Chr Start Location End Location Centimorgans (cM) SNPs
          3 110445556 127578737 16.0 4138
          5 2186412 5943342 12.2 1521
          6 126714774 147908309 21.8 4558
          18 48763478 66550278 26.2 4815

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          • #6
            There's not enough DNA shared for a full 2nd cousin relationship, I'm sure it's possible for 2nd cousins to share that little even less but highly unlikely.

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            • #7
              What is the best approach in trying to confirm a suspected 2nd cousin relationship, when the shared DNA with one suspect would seem to indicate a more distant relationship.

              My paper trail and family oral history would all seem to make a more distant relationship unlikely. I've examined the more distant relationship combinations and don't see any than make sense, other than 2nd cousin.

              Since both the subject and the match are from the paternal line, would a Y test help confirm or refute the relationship?

              Thanks

              Comment


              • #8
                Originally posted by dhorner View Post
                Thanks MMaddi.

                I did read that length of shared cM may be more important than the total. Do you have any insight on that? This is the information from GEDMatch for strings > 7cM. Maybe I'm just grasping at straws.


                Chr Start Location End Location Centimorgans (cM) SNPs
                3 110445556 127578737 16.0 4138
                5 2186412 5943342 12.2 1521
                6 126714774 147908309 21.8 4558
                18 48763478 66550278 26.2 4815
                If the shared DNA is in only 4 segments, that's an important bit of information in estimating the relationship.

                I and others have already posted that it's unlikely that the relationship of your uncle and his match is 2nd cousin. Only having 4 shared segments makes a 2nd cousin relationship even more unlikely.

                My sister shares 13 segments and I share 14 with our 2nd cousin. My sister shares 7 segments and I share 5 with our 2nd cousin, once removed.

                My sister and I both share 3 segments with our 3rd cousin. My sister shares 1 segment and I share 3 with our 3rd cousin, once removed.

                Since your uncle and his match only share 4 segments, that's much more in line with a 3rd cousin relationship or perhaps a weak DNA match for 2nd cousins, once removed.

                Comment


                • #9
                  I have a related question.

                  If established beyond any doubt 2nd cousins share 485 cM (with 15 segments longer than 10 cM), isn't it that some 2nd cousins of theirs would be squeezed out and would only have a chance to share much less than the average 193-338 cM ?

                  W. (Mr.)

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                  • #10
                    Perhaps only a 1/2 cousin

                    Any chance the ancestor had more than one wife and the two lines comes from a different mother?

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                    • #11
                      My Uncle and his match actually share 22 segments; the 4 I posted were the ones longer than 10cMs. Does that make much difference? All the posts I've read so far place a lot of emphasis on the total cMs being in the range 193-338 cM. Clearly, my Uncle's match is well below that mark at 115 cM, but I'm still trying to reconcile the paper trail to those results. If the match is truly a 2nd cousin, once removed; or a 3rd cousin, I'm having real trouble coming up with a plausible candidate for my Uncle's grandfather, based on age and/or location around the time of my Uncle's father's birth.

                      Any suggestions for another tactic to help verify?

                      Comment


                      • #12
                        So if I am understanding correctly the only two possibilities you were expecting based on geography etc. was a 2nd cousin or 1st cousin match between your uncle and the man you recruited to test? There is no possibility they are 3rd cousins I assume is what you are saying even if DNA points more to a 3rd cousin relationship. So 2nd cousin or 1st cousin would be what you were expecting, a second cousin match would mean your great grandfather was fathered by one of the other two sons of age of your great-great grandfather and a 1st cousin match meaning your uncle and match are from the same grandfather thus confirming your great grandfather. Correct? Like Canyon Wolf asked was there any way your assumed great-great grandfather had more than one wife where some of the children were half siblings?

                        Yes assuming they are both from the same assumed direct paternal line, I would do the Y-DNA on both men. Maybe the two men share the same great grandmother but different great grandfathers. Who knows maybe farmer Bob next door was the father of one of her sons meaning your uncle and the match are 1/2 2nd cousins. A Y-DNA test wouldn't confirm 2nd cousin or 3rd cousin etc. just so you know but it would at least tell you whether they are from the same paternal lineage or not. While you wait for results from that I would try to find another grandchild from one of the other two sons of your assumed great-great grandfather (not from the same son as the one you already tested) and see if they would do the Family Finder test, and see if they are a 1st or solid 2nd cousin match. I wouldn't give up on your theory as to who your great-great grandfather is, it seems like you are getting close but it needs a little more work.
                        Last edited by travers; 30 March 2015, 07:59 PM.

                        Comment


                        • #13
                          Originally posted by Canyon Wolf View Post
                          Any chance the ancestor had more than one wife and the two lines comes from a different mother?
                          None that I've found in the paper trail, but that isn't conclusive, by any means. I've been focusing on one of a group of brothers four generations back as my great-grandfather. Based on several comments, I probably need to move up the ancestor list another generation, and look at cousins to this group of brothers as additional suspects. That would address the inconsistently of the DNA results and the paper trail. I'm certain I'm in the right family, but finding the one that was my grandfather's father may be a riddle that continues to elude me.

                          Thanks for your input.

                          Comment


                          • #14
                            Originally posted by travers View Post
                            So if I am understanding correctly the only two possibilities you were expecting based on geography etc. was a 2nd cousin or 1st cousin match between your uncle and the man you recruited to test? There is no possibility they are 3rd cousins I assume is what you are saying even if DNA points more to a 3rd cousin relationship. So 2nd cousin or 1st cousin would be what you were expecting, a second cousin match would mean your great grandfather was fathered by one of the other two sons of age of your great-great grandfather and a 1st cousin match meaning your uncle and match are from the same grandfather thus confirming your great grandfather. Correct? Like Canyon Wolf asked was there any way your assumed great-great grandfather had more than one wife where some of the children were half siblings?

                            Yes assuming they are both from the same assumed direct paternal line, I would do the Y-DNA on both men. Maybe the two men share the same great grandmother but different great grandfathers. Who knows maybe farmer Bob next door was the father of one of her sons meaning your uncle and the match are 1/2 2nd cousins. A Y-DNA test wouldn't confirm 2nd cousin or 3rd cousin etc. just so you know but it would at least tell you whether they are from the same paternal lineage or not. While you wait for results from that I would try to find another grandchild from one of the other two sons of your assumed great-great grandfather (not from the same son as the one you already tested) and see if they would do the Family Finder test, and see if they are a 1st or solid 2nd cousin match. I wouldn't give up on your theory as to who your great-great grandfather is, it seems like you are getting close but it needs a little more work.
                            I think you stated my hypothesis in your first paragraph, but I'm looking to identify my great grandfather, whom I suspected was one of three brothers. My uncle's match coming in as a likely 3rd cousin, if correct, would effectively eliminate those 3 brothers as possibilities. I think I would need to move up another generation to cousins of those three brothers. That would address the seeming inconsistency between my original theory and the relationship results of my uncle and match. I will need to do more documentation on those cousins to see if I can locate a descendant willing to test. I would think that would confirm or refute my initial theory.

                            As for farmer Bob, I don't know about him fathering one of the brothers, but there certainly was a Farmer Bob in the picture with my Great Grandmother. That was the cause of the stonewalling I got from my Grandmother when I first embarked on this quest.

                            Thanks for your ideas...and for your encouragement.

                            David

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