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  • "In Common With"

    My main goal with DNA and genealogy is to find out as much as I can about my paternal great-grandfather; he was an orphan. My paternal uncle and I have both done Y testing here on FTDNA. The 'in common with' link' is of the greatest importance to me. I have it linked so there is a blue box on everyone who is related to my uncle. But, there are a number of my matches that I would think would be related to my uncle, it says they are not. Is it possible that they are related to him anyway? They have chromosone overlap.
    Last edited by TomFarrell; 4 March 2018, 04:06 AM.

  • #2
    The Family Finder test can't tell you absolutely that two people are not related. It can, however, give you very good odds that two people are not related as closely as about 4th cousins (roughly speaking, sharing common great-great-great-grandparents). The rule of thumb is that about 50% of actual 4th cousins will not show up as autosomal DNA matches using the default matching criteria, and about 10% of actual 3rd cousins won't match either.

    Given that situation, it is best to concentrate on the people who actually do match, because those are the ones where you have usable genetic evidence. The stronger the match, the better the genetic evidence. Pay attention to the size of the matching segments in centiMorgans (cM), avoid basing conclusions on segments under 10 cM.

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    • #3
      Originally posted by TomFarrell View Post
      I have it linked so there is a blue box on everyone who is related to my uncle. But, there are a number of my matches that I would think would be related to my uncle, it says they are not. Is it possible that they are related to him anyway? They have chromosone overlap.
      Blue box? Is this something you've created or do you mean the blue box used in the Matrix tool?

      You might find these two posts/articles by Roberta Estes helpful. The first focuses on why an apparent match isn't always a real match. It was written in 2013 but the science is still the same
      https://dna-explained.com/2013/12/15...nd-the-matrix/

      The second is a more recent guide to The Family Finder tools. Scroll down to find more on the In Common With and Matrix tools
      https://dna-explained.com/2016/07/21...mily-tree-dna/

      Hope this helps

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      • #4
        "In Common With"

        Thank you very much for your replies. Yes, it seems to be a matter of thresholds. That there may not be a large enough segment to be a match for my uncle. I read the articles. One of them mentions that for the purpose of phasing, the criteria is a bit higher than for ICW. I have my paternal uncle as a "linked relationship", that is where the blue boxes come from. They are very helpful. But, you will find that some of the ICW's do not quite qualify for a linked relationship.

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        • #5
          I have both of my parents linked (they both tested and I linked their relationship into my tree) and not every box is blue (paternal) or red (maternal.) The closest matches are the ones that are most designated, but the farther the match, they are less frequent. It's just the computer program, I guess, that some matches might be ambiguous and the program didn't want to commit to which side the person belonged.

          The go around on this for you is to find a known maternal "in common with." Even that isn't foolproof, but it's a starting point.

          They are all really nice tools. I use them frequently to find out how I might be related to someone. I also check the "in common with" on the "chromosome browser" and then also check things out over at GEDMatch.

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