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% dna shared vc. cM values

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  • % dna shared vc. cM values

    I have a chart that provides the predicted amount of shared dna that cousins should share. In the Family Finder results the amount of shared dna is provided as a cM figure.

    Is there a chart or conversion I can use to take the predicted amount of shared dna between say myself and my 3rd cousin once removed (should be "about" ~0.39%) and translates that into the amount of cM's?

    I want to use this information to assess whether a relative is showing an amount of shared cM that is in line with a "normal" inherited dna percentage or if in fact we are showing a higher cM value that might indicate that we are related along more than one line, ie. two of the other person's ancestor were related to me and not just one.

    Thanks.

    Jason

  • #2
    Use 7200 cM as a total. 0.39% would then be ~28 cM.

    I find the attached chart helpful although you will likely get a lot of other advice.
    Attached Files

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    • #3
      To convert each % to cMs, multiply by ~74.
      Last edited by Biblioteque; 10 March 2014, 07:32 AM. Reason: add

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      • #4
        Thanks for the info. Just what I was looking for.

        Jason

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        • #5
          Originally posted by marietta View Post
          To convert each % to cMs, multiply by ~74.
          How close would 35-60 cMs matches be?

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          • #6
            Originally posted by 1798 View Post
            How close would 35-60 cMs matches be?
            That's a difficult question.

            If you have a relative of known relation, say 3rd cousin, the chart mentioned above lists 0.78%, or 56cM, match. That's only the average of a wide distribution of matches that actually occur. 3rd cousins typically differ from 56cM by a lot.

            You're asking for someone who shows up as a match of 35-60 cM what they're relation might be. That's involves inverse probability, and it can't be computed from the direct probabilities.

            Although that chart shows that 3rd cousins are in that range, it's just as likely that match is a 4th or 5th cousins. The reason is that you have many times more 4th cousins, and many, many times more 5th cousins. Although the probability that a given 4th cousin shows up in that range may be 1/10 the probability that a given 3rd cousin shows up in that range, you've got 10 times as many 4th cousins as 3rd cousins.

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            • #7
              Originally posted by hansonrf View Post

              I find the attached chart helpful although you will likely get a lot of other advice.
              Very helpful chart, while I know what the % and cM data is, can any one tell me what the data after the cM means?

              the [email protected] as in Brother/Sister 50% 2700cM [email protected] or 1st cousins 12.5% 900cM [email protected]

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              • #8
                'around' 29 segments at avg 31 cM each. These are statistically what one might expect on average across large numbers of samples. Your results vary a good bit.

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                • #9
                  hansonrf thank you for the explanation

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                  • #10
                    Is it possible to say for certain whether this is a 3rd cousin or a 3rd cousin once removed?

                    Total shared 98.75 cM
                    3 longest segments: 39.36 cM, 13.21 cM, and 6.75 cM
                    number of shared segments 20

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                    • #11
                      How to read the chart

                      Im a bit confused how to read this chart. I have a 7.66% 1st-2nd Cousin prediction and Im not sure how to place him on this chart.
                      Originally posted by hansonrf View Post
                      Use 7200 cM as a total. 0.39% would then be ~28 cM.

                      I find the attached chart helpful although you will likely get a lot of other advice.

                      Comment


                      • #12
                        dna, who is a very generous person, posted this tool last week which will be helpful. You share approx 567 cMs with your match and the tool seems to lean toward 1st Cousin.

                        https://dnapainter.com/tools/sharedcm/1656
                        Last edited by Biblioteque; 17 November 2017, 04:30 PM.

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                        • #13
                          Originally posted by marietta View Post
                          dna, who is a very generous person, posted this tool last week which will be helpful. You share approx 567 cMs with your match and the tool seems to lean toward 1st Cousin.

                          https://dnapainter.com/tools/sharedcm/1656
                          Of course all the credit goes to the original author: Jonny Perl at DNA Painter https://dnapainter.com/ . He also has a very useful variation of the tool, see https://dnapainter.com/tools

                          And as always, please try to read https://isogg.org/wiki/Autosomal_DNA_statistics


                          Mr. W


                          P.S.
                          Even if it might have happened, that I had been the first to post the actual link in the forum, I know that I was not among the first people who wrote about it here.

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