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  • Half-Siblings?

    My sister and I did the Family Finder test. The results came back that we are half-siblings. I am wondering if this could be an error. I called FtDNA and asked about about the chances of it being an error, and was told that the possibility of us being full siblings was remote.

    The test showed that we shared 1750.63 cMs. I asked FtDNA what was the usual number for full siblings, and was told between 1900-2500.

    With a margin of error of +/-5 percent, the plus side would bring us up to 1838. I am just so unsure about this.

    I read that you can upload your results to GEDMATCH and perhaps get a clearer indication of our relationship, but, unfortunately, GEDMATCH seems to be down for now.

    I would appreciate any feedback on the subject. Also, does anyone have any idea about the lowest numbers for full siblings?

    Thank you very much.

    Wolfie

  • #2
    Try the following tool by David Pike

    http://www.math.mun.ca/~dapike/FF23utils/pair-comp.php

    Download your 2 Raw Data files, both have to be same Build either it be Build 36 or Build 37.

    Unzip and load into program (Data does not leave your computer, it just uses web browser to calculate)

    Copy and Paste Double Segment Match section if amounts are given
    Last edited by prairielad; 11 July 2014, 07:07 PM.

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    • #3
      Originally posted by Wolfie View Post
      My sister and I did the Family Finder test. The results came back that we are half-siblings. I am wondering if this could be an error. I called FtDNA and asked about about the chances of it being an error, and was told that the possibility of us being full siblings was remote.

      The test showed that we shared 1750.63 cMs. I asked FtDNA what was the usual number for full siblings, and was told between 1900-2500.

      With a margin of error of +/-5 percent, the plus side would bring us up to 1838. I am just so unsure about this.

      I read that you can upload your results to GEDMATCH and perhaps get a clearer indication of our relationship, but, unfortunately, GEDMATCH seems to be down for now.

      I would appreciate any feedback on the subject. Also, does anyone have any idea about the lowest numbers for full siblings?

      Thank you very much.

      Wolfie
      Are you both females? If you don't share the same father you can usually figure that out pretty fast if there are large holes in the X chromosome sharing.

      You can also download both of your raw data to David Pike's tool to see if you have any regions of full (double) match sharing too.
      http://www.math.mun.ca/~dapike/FF23utils/ Full sibs will have about 25% of full sharing where they match both the mother and the father in segments.
      Kathy

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      • #4
        Originally posted by Wolfie View Post
        My sister and I did the Family Finder test. The results came back that we are half-siblings. I am wondering if this could be an error. I called FtDNA and asked about about the chances of it being an error, and was told that the possibility of us being full siblings was remote.

        The test showed that we shared 1750.63 cMs. I asked FtDNA what was the usual number for full siblings, and was told between 1900-2500.

        With a margin of error of +/-5 percent, the plus side would bring us up to 1838. I am just so unsure about this.

        I read that you can upload your results to GEDMATCH and perhaps get a clearer indication of our relationship, but, unfortunately, GEDMATCH seems to be down for now.

        I would appreciate any feedback on the subject. Also, does anyone have any idea about the lowest numbers for full siblings?

        Thank you very much.

        Wolfie
        You can check here for actual statistics of people who got tested.

        https://docs.google.com/spreadsheet/...DaUE5dWc#gid=3

        Just click on the SIBLINGS tab. Unfortunately they've been putting only the % & number of segments. 39.7% was the smallest I saw.

        My maternal half-brother and I share 1770cM, 50 segments.

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        • #5
          Half-Siblings follow-up

          Thanks to all for your help.

          We are both female, and we don't match completely on the X Chromosome. Apparently, we do not have the same biological father.

          I looked at David Pike's Shared DNA Segments in Two Raw Data Files, and these were the only double segment matches:

          Chr 6 has a Double Segment Match of length 343 from position 27128307 to position 27884916 ( 0.76 Mb)
          Chr 6 has a Double Segment Match of length 594 from position 27936049 to position 28984512 ( 1.05 Mb)
          Chr 6 has a Double Segment Match of length 257 from position 29275507 to position 29522588 ( 0.25 Mb)
          Total Mb: 2.05

          Interestingly, we share some cousin matches (on FtDNA) that seem to be on the same paternal side. For instance, one cousin who matches us both, sent her family tree to me, and we shared several of the same ancestors on our paternal side.

          Thanks again for shedding some light on this mystery.

          Wolfie

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