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Genetic Distance vs Steps

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  • #16
    In the FTDNA Y DNA STR tests, the included "FTDNA Tip" information compensates for all differences in marker mutation rates, etc. It will calculate its prediction based on which markers do not match and by how much.

    http://www.familytreedna.com/faq-tip.aspx


    Matt.

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    • #17
      Originally posted by EdwardRHill View Post
      You count each difference as a single GD even if its on one marker. If you miss on other markers you count them as single GD giving you your total.

      Its the same way with steps every difference is counted as a single step even if it appears on the same marker. Count the differences gives you the number of steps.
      This is true for the most part, but in cases where you can show multiple mutations within one generation, as I can in my line, you can revise your GD to count all mutations within that one event as 1 GD even though it may show 4.

      This is where it is too your advantage at times to test different known lines to best determine what your correct GD should be. Results from 1 test can not tell you this and therefore automatically assumes these mutations happened at seperate times.

      So for a small group of testers as myself default results place our matches at a greater distance and omits other that maybe of interest.

      So when ever possible it is best to tests at least 2 known lines to "date" recent mutations to rule out a multiple marker mutation or two step mutation within 1 event (father to son)

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      • #18
        @mkdexter, thank you for the explanation. In my own mind I've now decided that the whole genetic distance thing is pretty much useless. I wish ysearch had TIP.

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        • #19
          Originally posted by prairielad View Post
          This is true for the most part, but in cases where you can show multiple mutations within one generation, as I can in my line, you can revise your GD to count all mutations within that one event as 1 GD even though it may show 4.

          This is where it is too your advantage at times to test different known lines to best determine what your correct GD should be. Results from 1 test can not tell you this and therefore automatically assumes these mutations happened at seperate times.

          So for a small group of testers as myself default results place our matches at a greater distance and omits other that maybe of interest.

          So when ever possible it is best to tests at least 2 known lines to "date" recent mutations to rule out a multiple marker mutation or two step mutation within 1 event (father to son)
          What is your source or sources?

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          • #20
            steps vs genetic distance

            Originally posted by efgen View Post
            To clarify this...

            Haplogroup Origins & Ancestral Origins do include samples from certain scientific/academic studies in addition to FTDNA customers. However, they do not include data from other commercial testing companies.

            Your right, I did read this too quickly. It makes sense now.

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            • #21
              Originally posted by EdwardRHill View Post
              What is your source or sources?
              I realise my statement might have been read the wrong way to what I was intending to say and apologize

              Yes, Genetic Distance is Genetic Distance in that the results give show how much of a genetic distance tester has to their matches (Each step difference = 1 GD). Genetically that is the difference between the two results.

              But for the sake of finding a common ancestor to matches, if the line that has tested has had multiply mutations in succession or within 1 generation(rarer but not unheard of) the Genetic Distance given will not give you the results you are hoping for with matches.

              This is what I was referring to, where to place your possible common ancestor, with matches. If you know that your line has gone through this situation, if you modify your GD you can use it personally to get a more accurate relationship to matches.

              Finding out if your line has had this situation requires testing multiple known lines, and as long as tester has tested these lines within their own account they can just use the line in which the mutations are not present for their research. But if they do not what I mentioned will aid in placing line within the more accurate timeframe for a common ancestor.

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              • #22
                Originally posted by prairielad View Post
                I realise my statement might have been read the wrong way to what I was intending to say and apologize

                Yes, Genetic Distance is Genetic Distance in that the results give show how much of a genetic distance tester has to their matches (Each step difference = 1 GD). Genetically that is the difference between the two results.

                But for the sake of finding a common ancestor to matches, if the line that has tested has had multiply mutations in succession or within 1 generation(rarer but not unheard of) the Genetic Distance given will not give you the results you are hoping for with matches.

                This is what I was referring to, where to place your possible common ancestor, with matches. If you know that your line has gone through this situation, if you modify your GD you can use it personally to get a more accurate relationship to matches.

                Finding out if your line has had this situation requires testing multiple known lines, and as long as tester has tested these lines within their own account they can just use the line in which the mutations are not present for their research. But if they do not what I mentioned will aid in placing line within the more accurate timeframe for a common ancestor.
                Thanks for the apology but no need to be sorry. I understood you, I just think it would be interesting to know the source behind what you said. I got my information from FTDNA FAQ. Do you have something you can share and we can all read? Its not that I don't believe you I just figured the article or other source would be interesting for us all to read. It will probably help some of us that qualify for this circumstance but don't know we do qualify.

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                • #23
                  I remain unconvinced.

                  I remain unconvinced about TMRCA and genetic distance. I have privately messaged couple of individuals about this and to date one answered and one did not. The one who did answer affirmed my concerns about how TMRCA is calculated with regard to genetic distance.

                  When genealogical genetic testing became commercially available on a widespread basis we were only testing 12 markers. At that point, TMRCA would tell us convincingly that a mismatch = 0-2 would confirm relationship within a genealogical timeframe. Of course we are now capable of testing way beyond the twelve marker constraints of yore and it gives me cause to wonder if the algorithms were or need to be changed to keep pace. Someone who was a GD=3 @ 12 markers would not be considered to be a relevant match, however, a gd=3 @ 111, probably would be. Now that we have upgraded our capabilities I am curious to know about the impacts of the calculations as we knew them to be. We also must take into account generational calculations. My average generation is closer to thirty years than it is to 20. Would this also impact TMRCA?

                  Please Note: I am not discussing mutation rates. However, I do have a question regarding methodology in discussing those. Does anyone know what the methodology was in determining the mutation rates that are now academic and scientific fact?

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                  • #24
                    Im not sure this belongs in this thread but I have a question about steps,names...matches.
                    I can find answers to questions that relate to distance,steps etc when it comes to same surname but what if surname is different. For instance I have a match on y dna that shows no surname and under markers compared shows 14 with genetic distance of 2. Is that actually the true genetic distance? I am very new to this was full steam ahead after I got our dna results but then just gave up as somewhat complicated .
                    Thanks

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                    • #25
                      I'm always trying to correlate genetic steps to levels (or branches) of my family tree, i.e., a 1-step difference could be an uncle while a 2-step difference would be 1 level up from the uncle, along that tree's generation. Am I making sense?

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                      • #26
                        To me, your parents would be one step, and then your uncle would be two steps. Your 1st cousin would be three steps, as well as your great uncle (who would be one level up from your uncle).

                        LivingDNA has a chart for this. There might be others out there. Steps called degrees on the LDNA chart.

                        Centimorgan Chart: Understanding DNA Relationships | Living DNA‚Äč

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                        • #27
                          Why do you think so? I think both are on the same step.

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                          • #28
                            You are right. I veered off into autosomal steps. If you are looking at Y DNA, then each generation would be a step. Although not to be confused with marker values or genetic distance.

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