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Determining Lines of Descent on genome

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  • Determining Lines of Descent on genome

    My husband, son and I have all tested on FTDNA and when I look at my son's genome on the Chromosome Browser he shows matches on each of his chromosomes from both his father and me which line up exactly. How can I determine which parts of his genome come from my side of the family and which from my husband's? I realize that I am looking at a 2 dimensional representation of his genome which is actually three dimensional, but is there a way to map specific segments?

  • #2
    Gedmatch enables people to phase their results with their parents to determine which parent contributed which side of each chromosome.

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    • #3
      Originally posted by CTlibrarian View Post
      My husband, son and I have all tested on FTDNA and when I look at my son's genome on the Chromosome Browser he shows matches on each of his chromosomes from both his father and me which line up exactly. How can I determine which parts of his genome come from my side of the family and which from my husband's? I realize that I am looking at a 2 dimensional representation of his genome which is actually three dimensional, but is there a way to map specific segments?
      Not directly. However, if you look at your matches, you'll notice that your son has inherited just a subset of your matches. You can't give him all of your DNA, so you give him a combination of what you inherited from your parents.

      Let's say you have a bunch of people who match you on chromosome 15 between 10 and 20 Mb. You may be able to divide this group into two parts, the ones who match your son for all or part of the segment, and the ones who don't match your son. Cluster one will come from one of your parents, and cluster two from the other parent. You will not know which is which unless you find known cousin from your paternal or maternal side.

      I'm glossing over some of the complications and marginal cases, but that's the basic idea.

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      • #4
        Thank you for your responses. I have uploaded my son's results to Gedmatch, awhile ago it seems, but they have yet to be tokenized and processed. Did I miss a step?

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        • #5
          The issue is that we have two copies of each chromosome but there isn't any way to tell based on one person alone which one came from each parent. In your case, since both you and your husband have tested, the easiest way to tell which side of the family a match comes from is simply to check whether the person matches you or your husband. In general unless you and your husband are distantly related, a person will not likely match both of you on the same segment so it should be clear whether the match is from your side or your husbands.

          In cases where the parents haven't tested, you can only check if the two people you match match each other to see if they are from the same chromosome copy or if one is from the paternal and the other the maternal chromosome.

          Regarding GedMatch, there's a tool that can be applied after you've uploaded all three of your DNA kits that can be used to 'phase' your sons results and essentially separate the DNA data into two kits that only contain one chromosome copy each rather than containing the info for both chromosome versions. So you would end up with one kit being your son's DNA that he got from you and another kit being the other half of your sons DNA that he got from your husband.

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          • #6
            This is slightly off topic since it refers to Gedmatch rather than FTDNA, but has anyone had difficulties uploading results? I have emailed the administrator, but his reply didn't really solve the problem.
            I downloaded the Build 36 Autosomnal Raw Data and Build 36 X Autosomnal Raw Data and then attempted to upload them to Gedmatch. I got the first batch in successfully, but when I attempted to upload the x chromosome data I got the message that "(381) Autosomnal for this kit number has been previously loaded." However, when I run the DNA File Diagnostic Utility it shows that there is no x chromosome data. This has happened 4 times with 3 different kits. Have I missed a step?

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            • #7
              I would suggest logging in to Gedmatch and go to the EDIT or DELETE your DNA resource profiles and delete each kit that you are having an issue with.

              Then redownload a fresh copy of both your Build 36 autosomal and build 36 X Raw Data from FTDNA.(save, do not open)

              Then try uploading them to Gedmatch again (compressed files)

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              • #8
                Thanks. That worked.

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