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Looking for a Tool or Feature to

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  • Looking for a Tool or Feature to

    If, on a given Chromosome, I have determined starting point and ending point of where two or more matches overlap -- is there anyplace I can look to plug in that starting and ending point on that Chromosome to get the cMs for it?

  • #2

    Select chromosome
    Select Build number (FTDNA positions are build 36, other companies and gedmatch genesis use build 37)
    Select "Physical positions (bp) only"

    In Paste Query box see images attached
    Attached Files


    • #3
      Part 2 to interpolator

      See image
      Attached Files
      Last edited by prairielad; 3rd April 2019, 07:50 PM.


      • #4
        I agree, it would be pretty cool if at least one of the major DNA genealogy sites could package the genetic map interpolation function in a user-friendly way, as a tool accessible directly from their chromosome browser and/or chromosome painter.


        • #5
          Originally posted by prairielad View Post

          Select Build number (FTDNA positions are build 36, other companies and gedmatch genesis use build 37)
          Thanks much!! A couple of questions tho -
          I could have sworn, a number of years ago, FTDNA upgraded/changed the Build Number it used. Am I mis-remembering, or??

          Also - am not getting very good correlation to FTDNA when plug in the start and end numbers of actual segments they report -
          For a Chr6 segment FTDNA says is 23.41 I got 23.178 if Build 36, 23.056 if Build 37.3
          For a Chr8 segment FTDNA says is 5.02 I got 2.399 if Build 36, 2.38 if Build 37.3

          It looks like it was giving much closer results to Gedmatch -- are others seeing something similar, or ??


          • #6
            I recall that FTDNA does something funny with SNP's for purposes of identifying matching autosomal segments, grouping them into blocks of 100 rather than treating them individually. Depending how they do this, perhaps that's the explanation for the discrepancies you noted.

            Another potential problem is that there is actually a male and a female genetic map, because there is significantly less recombination in human males generally (not sure whether the difference is equally distributed all over the 22 autosomes). I believe FTDNA and other vendors probably use the "average" map (average of male and female statistics?) -- that would seem to make the best sense.


            • #7
              FamilytreeDNA uses Build 37 internally, but position numbers displayed in chromosome browser are still displayed as Build 36 positions.
              This may cause the discrepancy if they are using Build 37 to calculate cM, but displaying segment start stop points in browser as Build 36

              As John McCoy states, I do not know if at FTDNA they uses Gender related cM values or the sex average
              ie)Female to Female comparison (Female cM amount)
              Male to Male (Male cM amount)
              Male to Female (sex average cM amount)

              I also don't know if there is a standard model for figuring out cM, there maybe slightly different scientific models then the one I linked.
              Last edited by prairielad; 5th April 2019, 05:07 PM.


              • #8
                If you wish to convert FamilytreeDNA positions (old Gedmatch site also displays Build 36 Positions), the following can be used to convert
                Attached Files
                Last edited by prairielad; 5th April 2019, 05:15 PM.