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Mapping your Autosomal DNA?

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  • Mapping your Autosomal DNA?

    Hello again,

    I have yet another question. I am curious if adding up all the CM of a particular family if I can get a percent of that family. For example:

    Say I have 66.2 total Cm of the Kelly family, would it be possible to turn that into a percent to say that I have _% of Kelly DNA in my known results?

    If possible this sounds fun!

  • #2
    Originally posted by DavdJ View Post
    Hello again,

    I have yet another question. I am curious if adding up all the CM of a particular family if I can get a percent of that family. For example:

    Say I have 66.2 total Cm of the Kelly family, would it be possible to turn that into a percent to say that I have _% of Kelly DNA in my known results?

    If possible this sounds fun!
    Short answer: no.

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    • #3
      hehe no problem. Thanks much

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      • #4
        Actually, I don't see why not? 23andMe gives a percentage of the DNA you share with each match and ISOGG has instructions on how to figure it out on FTDNA:

        "23andMe provide information on both the percentage of DNA shared and the number of shared cMs. FTDNA do not provide percentages and only provide information on the number of shared cMs. The following table shows the FTDNA Family Finder cM data for comparison purposes. When using Family Finder data the calculation can also be made by dividing the total number of autosomal cMs by 68 to get the percentage of the autosomal genome that two people share. Note that the FTDNA figures exclude the X-chromosome cMs. Males have one X-chromosome and females have two X-chromosomes. If you want to include the X-chromosome in the calculations, then there are 7158.06 cMs in the entire genome if you are a female. Therefore divide the total number of cMs by 71.6 to get the percentage of the entire genome that two people share. If you are a male there are 6962.13 cMs when combining the atDNA with the X-chromosome."

        http://www.isogg.org/wiki/Autosomal_DNA_statistics

        If you can determine your shared ancestry with more than one person with confidence and accuracy, I don't see why you can't calculate the total amount that you share with all those people and figure out the percentage.

        Just be careful not to simply add the total amount you share with all of them together because there may be overlapping segments. If you match three people from your Smith line on one segment of 50 cMs, that's not 150 cMs you inherited from the Smith line, it's only 50 cMs.

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        • #5
          I would say that theoretically it would be possible. However, you would need to find a lot of matches with people descended from the same ancestor and carefully calculate the shared DNA involved in the various segments, as Germanica details.

          At this point in time, I don't think there are enough people in the three autosomal testing companies' databases to assure that you can find all the segments you have that came from a specific ancestor. It sounds like, while theoretically possible, in practice it couldn't be done with the accuracy needed.

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          • #6
            Neato! The reason I asked is because I'm curious how much I inherited from different ancestors versus my parents. I understand what you folks are saying :} I'll be careful

            If anything, it could range from close to a fair estimate.
            Last edited by DavdJ; 14 December 2014, 11:43 AM.

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            • #7
              Originally posted by DavdJ View Post
              Neato! The reason I asked is because I'm curious how much I inherited from different ancestors versus my parents.
              I'm not really sure what you mean - all your DNA came from your parents. But it also all came from more distance ancestors because your parents DNA came from them. They are one in the same.

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              • #8
                ah, are you saying I have every single segment that my father has for example? I was under the impression that the automosal DNA results were random, even for father and son.

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                • #9
                  Not sure why you think the others are versus your parents. You parents got their DNA from the more distant ancestors. You will not have anything from them that one of your parents does not have.

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                  • #10
                    Originally posted by LynCra View Post
                    Not sure why you think the others are versus your parents. You parents got their DNA from the more distant ancestors. You will not have anything from them that one of your parents does not have.
                    Yes, and it might on occasions only appear in the Family Finder that you got something that your parents do not have.

                    Specifically when you got two or more adjacent segments from both parents and that combined total is matching somebody in its entirety.

                    W.

                    P.S. Somebody described the above scenarios in detail. Maybe someone remembers and will add the link.

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                    • #11
                      Originally posted by DavdJ View Post
                      ah, are you saying I have every single segment that my father has for example? I was under the impression that the automosal DNA results were random, even for father and son.
                      You will share basically 50% of DNA with each of your parents. That means that your father has 50% of his DNA that didn't show up in you and the same for your mother.

                      Although you can never recover all the DNA you didn't receive from each parent, testing as many of your siblings as possible will get you closer to 100% of your parents' DNA. (Although you share 50% of your DNA with full siblings, they received different segments of DNA from your parents than you did in the 50% they don't share with you.) The more siblings you can test, the closer to finding 100% of your parents' DNA you will get.

                      But there's an easier way to get all your parents' DNA. If they're alive and willing to test, have them test. Or am I misunderstanding what you're trying to accomplish?

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                      • #12
                        Thanks folks,

                        I appreciate the feedback :}. Yes, I think what made me think that it was from different ancestors is that I had an entire segment that my father didn't have.

                        My father also has longer segments with most older ancestors than I do.

                        I started to play around with the percentages as a test for one of my ancestors, let's call him John. His CM is 66.2 and the percentage turned out to be 97% percent. Is this correct? how can one ancestor be that high? I'm not knowledgeable enough with this aspect to know if I did it correctly.
                        Last edited by DavdJ; 14 December 2014, 07:52 PM.

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                        • #13
                          Clear as water Mmadi :] Thanks for the explanation. I understand now. I just had a misunderstanding on my part.

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                          • #14
                            Originally posted by DavdJ View Post
                            Thanks folks,

                            I appreciate the feedback :}. Yes, I think what made me think that it was from different ancestors is that I had segment that my father didn't have.

                            My father also has longer segments with most older ancestors than I do.

                            I started to play around with the percentages as a test for one of my ancestors, let's call him John. His CM is 66.2 and the percentage turned out to be 97% percent. Is this correct? how can one ancestor be that high? I'm not knowledgeable enough with this aspect to know if I did it correctly.
                            66.2/6766.2=0.0097=0.97% or rounded up 1%

                            On average that is a fourth cousin once removed but could actually be from further back in the tree.

                            If John is related to you through your father's side some segments will be longer when comparing John and your father and the total will be larger. If John doesn't show as a match to your father then he should be related to you through your mother.

                            You've been give the link before by Germanica but here it is again - http://www.isogg.org/wiki/Autosomal_DNA_statistics

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                            • #15
                              Originally posted by DavdJ View Post

                              I started to play around with the percentages as a test for one of my ancestors, let's call him John. His CM is 66.2 and the percentage turned out to be 97% percent. Is this correct? how can one ancestor be that high? I'm not knowledgeable enough with this aspect to know if I did it correctly.
                              Clearly you're doing something wrong. No one shares 97% of their DNA with someone who's not an identical twin of the person. Identical twins should share 100%.

                              Parents/children and full siblings share about 50%, more or less. I don't think you'll find any cases where much over 60% is shared. Grandparents/grandchildren, aunt-uncle/nephew-niece and half-siblings share about 25%.

                              There's just no way to share 97% with someone more distant than these close relatives. Due to recombination, the percentage coming from a specific ancestor declines as the relationship is more distant.

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