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1st Cousin once removed but 234cMs

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  • 1st Cousin once removed but 234cMs

    Hi,

    I recently did my DNA test, and I found a 1st cousin once removed, but the shared DNA is 234cMs. I'm guessing the most likely reason for this is a break in the line, either my great-grandfather is not related, to me, or not related to her? Is there any other way the cMs would be so low between us?

    We've spoken, and confirmed she is the daughter of my great-aunt. (I never knew any of my dads family, so having any cousins on my father's side is new to me).

    Kind regards

  • #2
    Here is an article about autosomal testing and cousins:

    https://dna-explained.com/2013/10/21...onships-wrong/

    Comment


    • #3
      toaster, If you use the Shared cM Project Tool, and enter 234 cM, it will show various relationship possibilities. For 234 cM, it doesn't show 1C1R (first cousin once removed), but does show first cousin twice removed, and half 1C1R as possible relationships. You should also note that in the accompanying chart for 234 cM, while the "average" shared amount of cM is 439 for 1C1R, the range of possible shared cM is actually 141 – 851 cM. So, your 1C1R does fall within the reported range for 1C1R, as well as that for half 1C1R; he or she could be either. I wouldn't necessarily jump to the conclusion that there was a break in the line.

      It is the same with the DNA Detectives Autosomal Statistics Chart, where they show a range for 1C1R of 215-650 cM shared, in their "Group D," but 234 cM also could fit in Groups E or F. Another link to the chart is in a post by The DNA Geek, "The Limits of Predicting Relationships Using DNA," which is worth a read for your situation. As she says at the beginning of that post,
      The one thing we genealogists probably want most from our autosomal DNA matches is something they can’t give us: an exact relationship prediction based on shared DNA alone. Unfortunately, with the exceptions of identical-twin, parent–child and full-sibling matches, that’s simply not possible.
      She then goes on to explain why this is so.

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      • #4
        As you know from this discussion, the shared cM value usually gives you a range of possible relationships. At this time, you don't have any evidence to tell you that the 1C1R relationship is wrong. You could possibly obtain additional evidence to rule out one or more of the possible relationships by testing other relatives. However, if it were my family, I would not want to suggest that something was amiss without carefully considering how this information might affect them.

        Comment


        • #5
          I share with one 1C1R - 309 cMs.
          With another 1C1R, I share 502 CMs.

          That is the low and high spread. I have many matches 1C1R in between those ranges.

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          • #6
            I recalled one more thing. You should check how your first cousin once removed matches you in the Chromosome Browser. Then, look at the tab, "Detailed Information," which will show how many cM you match on each segment. You can download this information, then sort by total cM.

            Next, remove all segments that are less than 7 cM, and add up the rest (those that are 7 cM and larger). This will give you a more accurate total to use to determine the likely relationship possibilities.

            FTDNA uses ALL matching segments, no matter how small, to add to the total cM shared. This gives a misleading total in many cases. No other genetic genealogy DNA testing company does this.
            Last edited by KATM; 30 January 2020, 04:21 PM.

            Comment


            • #7
              Originally posted by KATM View Post
              toaster, If you use the Shared cM Project Tool, and enter 234 cM, it will show various relationship possibilities. For 234 cM, it doesn't show 1C1R (first cousin once removed), but does show first cousin twice removed, and half 1C1R as possible relationships. You should also note that in the accompanying chart for 234 cM, while the "average" shared amount of cM is 439 for 1C1R, the range of possible shared cM is actually 141 – 851 cM. So, your 1C1R does fall within the reported range for 1C1R, as well as that for half 1C1R; he or she could be either. I wouldn't necessarily jump to the conclusion that there was a break in the line.

              It is the same with the DNA Detectives Autosomal Statistics Chart, where they show a range for 1C1R of 215-650 cM shared, in their "Group D," but 234 cM also could fit in Groups E or F. Another link to the chart is in a post by The DNA Geek, "The Limits of Predicting Relationships Using DNA," which is worth a read for your situation. As she says at the beginning of that post,

              She then goes on to explain why this is so.
              Yes, well she is definitely my grandfather's sister's daughter (making her my 1st cousin once removed), and the DNA match is still within that range, so for now I can assume that we a full 1st cousins once removed, and not half.

              Originally posted by KATM View Post
              I recalled one more thing. You should check how your first cousin once removed matches you in the Chromosome Browser. Then, look at the tab, "Detailed Information," which will show how many cM you match on each segment. You can download this information, then sort by total cM.

              Next, remove all segments that are less than 7 cM, and add up the rest (those that are 7 cM and larger). This will give you a more accurate total to use to determine the likely relationship possibilities.

              FTDNA uses ALL matching segments, no matter how small, to add to the total cM shared. This gives a misleading total in many cases. No other genetic genealogy DNA testing company does this.
              The match was made on AncestryDNA, her DNA is not on FTDNA.

              Originally posted by John McCoy View Post
              As you know from this discussion, the shared cM value usually gives you a range of possible relationships. At this time, you don't have any evidence to tell you that the 1C1R relationship is wrong. You could possibly obtain additional evidence to rule out one or more of the possible relationships by testing other relatives. However, if it were my family, I would not want to suggest that something was amiss without carefully considering how this information might affect them.
              Certainly - even if I find solid 100% proof that there is a break on either side, I wouldn't dream of bringing it up with her. If, however, there is a break on my side, then I would like to know, so I can trace my ancestors.

              As I said before, I had no contact with my father's side of the family, so I'm just trying to piece together what I can, from what I've got. To make things worse, my paternal g-grandparents were born outside of the UK, and there are hardly any surviving records, and currently no DNA matches which link with what I currently know of their ancestry.

              Thanks everyone for the responses!

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