Announcement

Collapse
No announcement yet.

I thought we were cousins...?

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

  • I thought we were cousins...?

    Hi Folks,

    I have a known 4th cousin whom I convinced to get the family finder test, and we are not coming up as matches for each other.

    Is this common? Or is one of us not related in the way we think that we are?

    To be more specific, her maternal grandmother's paternal grandmother was siblings with my paternal grandmother's paternal grandfather...or so we think...

    Can anyone advise?

    Thanks,
    Scott

  • #2
    Because of recombination over the generations in both lines, only about 50% of 4th cousins share enough DNA to be declared a match in an autosomal DNA test. So, you and your 4th cousin probably fall in the 50% who don't share enough DNA to be considered a match.

    Although autosomal tests can find 5th and more distant cousins, it's only reliable out to about 3rd cousins. The figure for 2nd cousins is about 99% sharing enough DNA to be declared a match. It's about 90% for 3rd cousins.

    Comment


    • #3
      Scott, try uploading both datasets to Gedmatch.com and then comparing them one-to-one with a very small segment size, 1 cM. Please post whether you find any shared segments that way.

      Comment


      • #4
        Originally posted by J Honeychuck View Post
        comparing them one-to-one with a very small segment size, 1 cM.
        1 cM isn't a good threshold to use. Practically everybody matches everybody else at that low level, on many segments scattered all over the place.

        Segments sized 6, 7, and 8 cM are more valuable. They can easily be disregarded by Family Finder when the 20 cM minimum total criteria isn't met by a matching pair, but there are ways to validate some of those segments inside GEDmatch, while others of those lengths turn out to be false.

        Comment


        • #5
          On GEDmatch, you can also look for people who match both of you, and you may find closer cousins to either one of you. Serendipity seems to strike fairly often on GEDmatch.

          Comment


          • #6
            I want to know if Scott does not share any DNA at the 1cM level.

            Comment


            • #7
              This isn't uncommon.

              I have two sisters that match a third cousin but with less than average DNA for the relationship. They don't match their 3rd cousin's niece and nephew on FTDNA nor Gedmatch.

              On another line the sisters match a 4C1R at Gedmatch (he tested with another company). Recently his aunt's kit was uploaded (so 4C to the sisters) and she only matches one of them.

              I had high hopes that a 1/2 3rd cousin would match another kit. They don't match on FtDNA but on Gedmatch share a 9cM segment, a 5cM segment and a few 3-4cM segments.

              Comment


              • #8
                Update from OP

                Hi folks,

                Thanks for your suggestions and input.

                I've had my cousin join GEDMATCH, and I set the threshhold to a variety of #s. When I set it to 4 (or below), I do get matches with her.

                At 4cm threshhold, we match at 4.9, 4.8 and 4.8 across three different chromosomes (1, 4, 13, respectively).

                I think I understand this process a whole lot better from this exercise, and from your feedback. Thank you very much.

                Scott

                Comment


                • #9
                  Maybe 1 of those 3 segments are real of course it's possible they are all false. Either way I personally wouldn't draw any conclusions from them, but that's me. If the paper trail is solid between the two of you I wouldn't see any reason to doubt it and the DNA neither confirms or denies anything so I would just go with the paper trail.

                  Comment


                  • #10
                    Originally posted by lobsterjesus View Post
                    Hi folks,

                    Thanks for your suggestions and input.

                    I've had my cousin join GEDMATCH, and I set the threshhold to a variety of #s. When I set it to 4 (or below), I do get matches with her.

                    At 4cm threshhold, we match at 4.9, 4.8 and 4.8 across three different chromosomes (1, 4, 13, respectively).

                    I think I understand this process a whole lot better from this exercise, and from your feedback. Thank you very much.

                    Scott
                    I had the Sanme thing happen w a paper trail cousin. Did not match me. Would have been a 3rd cousin once removed. However, when I had my mom tested he popped up in her list. We also share numerous unknown close matches and if I do the list option on gedmatch for a match to see who their matches are he is in the majority of my matches. I guess I just didn't inherit any matching cM's w him.

                    Comment


                    • #11
                      A couple of relatives share a good 40+cM segment with a 1/2 3C1R . She wasn't even on my radar when she popped up as a very weak match on the first kits I manage (even with a family name I know, but on her tree the location was too vague)


                      The relative with the 44cM+ segment did comment that maybe they got more from this line. I wouldn't draw that conclusion. All it means is that they and the 1/2 3C1R got the SAME segment from their mutual gtgtgt-grandfather (and a 4C got most of it too). Other descendants most likely have similar amounts from the mutual ancestor. Just not ones that match so well.

                      Comment


                      • #12
                        First Cousin 1R

                        Originally posted by MMaddi View Post
                        Because of recombination over the generations in both lines, only about 50% of 4th cousins share enough DNA to be declared a match in an autosomal DNA test. So, you and your 4th cousin probably fall in the 50% who don't share enough DNA to be considered a match.

                        Although autosomal tests can find 5th and more distant cousins, it's only reliable out to about 3rd cousins. The figure for 2nd cousins is about 99% sharing enough DNA to be declared a match. It's about 90% for 3rd cousins.
                        Michael, can you tell me what the % of matches should be for 1st cousin 1R? I have a 1C1R who tested and we have no matches on FTDNA. Something not right methinks?

                        Comment


                        • #13
                          Originally posted by T0pcat View Post
                          Michael, can you tell me what the % of matches should be for 1st cousin 1R? I have a 1C1R who tested and we have no matches on FTDNA. Something not right methinks?
                          Virtually every set of 1st cousin 1R should come up as close matches. If the two of you aren't on each other's match list, then something is definitely amiss. One or the other of you may not be the biological offspring of a parent who raised you.

                          The easiest thing to do to check out if you two are related is for both of you to upload your raw data to GEDmatch, where you can directly compare to each other. Then you can see if there are shared segments of 7.0 cM or more. If not, that confirms one of you has an NPE.

                          Comment


                          • #14
                            Originally posted by MMaddi View Post
                            Virtually every set of 1st cousin 1R should come up as close matches. If the two of you aren't on each other's match list, then something is definitely amiss. One or the other of you may not be the biological offspring of a parent who raised you.

                            The easiest thing to do to check out if you two are related is for both of you to upload your raw data to GEDmatch, where you can directly compare to each other. Then you can see if there are shared segments of 7.0 cM or more. If not, that confirms one of you has an NPE.
                            Thanks Michael, that's what I was afraid of. I'm on Gedmatch so I'll have to persuade my cousin to upload hers. Looks like one of us could be in for an unfortunate surprise!

                            Comment


                            • #15
                              Originally posted by T0pcat View Post
                              Thanks Michael, that's what I was afraid of. I'm on Gedmatch so I'll have to persuade my cousin to upload hers. Looks like one of us could be in for an unfortunate surprise!
                              I should add that the NPE may not involve you or your cousin. It may involve your relevant parent or her relevant parent.

                              Comment

                              Working...
                              X