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Using NON X-match strategy to Find MRCA

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  • Using NON X-match strategy to Find MRCA

    My mother is a match to KB as a 2nd-4th cousin in the FTDNA autosomal Family Finder match list.

    I've strategized that if KB is NOT an X-match, then I can rule out any lines that contributed X to my mother. Attached is an image of the Xlines I've ruled out because they are X-matches to my mother.

    Questions:
    1) I have ruled out the Charles G line, but I'm wondering if I should follow his father's line?
    2) Are there any major errors in this strategy that I need to correct?

    Weird Twist of Events:
    KB and I decided to upload my mother's tree to ancestry and attach KB's DNA file to it in my mother's "place" in the tree, just to see what matches came up. This resulted in a match from ancestry.com on the Mary A line!!!! But Mary A is an X-match to my mother. So how is it that FTDNA says KB and my mom are NOT X-matches, yet ancestry.com says they are? Gedmatch also says KB and my mom DO NOT match on Xchromosome.

    What am I missing?
    Attached Files

  • #2
    X can only be used as an aid in determining which line IF one has an acceptable sized segment which matches.

    Not matching on X means nothing, match can still be any line. Many factors contribute to not sharing.

    What size is the X share? Most segments under 7cM are false...

    Comment


    • #3
      Gedmatch default compare only shows segments 7cM or greater. One needs to adjusts the default cM and SNP thresholds to see smaller segments (which have a high chance of being false). Try setting X one to one defaults to 3cM and 300 SNPs

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      • #4
        You are making a error with your X non-matching assumptions.

        Matching is the key data that your want to investigate. Non-matching data might be looked at when the relatives are extremely close, but the real goal is to investigate matches.

        FTDNA will show X matching on its display, but X plays no role in its relationship calculations.

        On FTDNA, do a chromosome browser display of KB to your mother and you will find a segment of 7 cM or higher on chromosomes 1 to 22 that is causing the match.

        The exercise on Ancestry seems to have picked up someone along the Mary line. Have that person at least upload to Gedmatch. Now do a 3 way lookup on Gedmatch of KB, your mother and the third person and see if the segment is the same. If yes, continue your pursuit of the Mary line as probably correct. You could also ask the new person to transfer to FTDNA, but they will have to be about a 3rd cousin or better to have a match. Gedmatch will be able to compare in any event.

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        • #5
          Originally posted by ech124 View Post
          Have that person at least upload to Gedmatch.
          ech124

          Would you please tell me what wording you use in your messages to get people to upload to Gedmatch? I haven't had any success at all in getting people to upload.

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          • #6
            Originally posted by MoberlyDrake View Post
            ech124

            Would you please tell me what wording you use in your messages to get people to upload to Gedmatch? I haven't had any success at all in getting people to upload.
            I think you have to get the hook set before your bring up GEDmatch.

            Jack

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            • #7
              Originally posted by prairielad View Post
              X can only be used as an aid in determining which line IF one has an acceptable sized segment which matches.

              Not matching on X means nothing, match can still be any line. Many factors contribute to not sharing.

              What size is the X share? Most segments under 7cM are false...
              I'm not sure I agree with you that it means nothing. If we have subset of "matches" and some of those matches are "X", they all go in the same pool because they are XMATCHES. Conversely, the remaining pool of "matches" would go in the pool named "NON XMATCH". So I do think it can mean something..at the very least it means I can rule out the pool of XMATCHES.

              The longest cM is 11.4 on Chr 9. the est to MCRA is 5.2 generations.

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              • #8
                When I ask my matches to upload to Gedmatch, I tell them it is FREE; and it takes less than 10 minutes.

                This works for me.
                Last edited by Biblioteque; 17th August 2017, 01:10 PM.

                Comment


                • #9
                  Originally posted by ech124 View Post
                  You are making a error with your X non-matching assumptions.

                  Matching is the key data that your want to investigate. Non-matching data might be looked at when the relatives are extremely close, but the real goal is to investigate matches.

                  FTDNA will show X matching on its display, but X plays no role in its relationship calculations.

                  On FTDNA, do a chromosome browser display of KB to your mother and you will find a segment of 7 cM or higher on chromosomes 1 to 22 that is causing the match.

                  The exercise on Ancestry seems to have picked up someone along the Mary line. Have that person at least upload to Gedmatch. Now do a 3 way lookup on Gedmatch of KB, your mother and the third person and see if the segment is the same. If yes, continue your pursuit of the Mary line as probably correct. You could also ask the new person to transfer to FTDNA, but they will have to be about a 3rd cousin or better to have a match. Gedmatch will be able to compare in any event.
                  How do you know Xmatching plays no role? I'd like to understand your reasoning...are you saying that when FTDNA puts it in the FF match list it means nothing? As explained I'm looking to rule out the Xmatches so I can concentrate on the NON-Xmatches, so it is important to look at the NONs in this scenario.

                  I've done the match you suggested. Longest segment is 11.4 on Chr 9 (obviously not an X-match).

                  On the triangulation idea...worth a try.

                  My brother also matches KB on Chr 9, but I do not. That means to me that I didn't inherit the exact same DNA that my brother did on that Chr 9, or I have it, but it's too small to measure. To test this last assumption, I compared myself to KB in gedmatch and reduced the threshold to 1 cM...the only match I got was on Chr 14 at 2 cMs. I KNOW KB and I are related because my brother and mother are matching.

                  I think all chromosomes act in the same way, ie. if there is a match at Chr 9 (like above), then all other non Chr 9 matches could technically be ruled out...that's the same strategy I'm trying to apply to X. If there is an XMATCH, then all other matches are NON X-match. Granted there could be very small amounts not transferred down and to me those go in the too small to be credible category.

                  I don't think looking at the inverse of "matches" is worthless, esp. when there is no other information available. But I am trying to understand why the ancestry.com matching algorithm comes up with an XMatch when FTDNA and Gedmatch do not.

                  Comment


                  • #10
                    Originally posted by MoberlyDrake View Post
                    ech124

                    Would you please tell me what wording you use in your messages to get people to upload to Gedmatch? I haven't had any success at all in getting people to upload.
                    that's been my experience too.

                    Comment


                    • #11
                      Within the context of FTDNA, X-DNA is not treated like the other chromosomes. I don't know how ancestry.com looks at it, but they do not have a chromosome browser so that is a big disadvantage when seeking DNA proof.

                      Here is the FAQ here, so read it very carefully:


                      https://www.familytreedna.com/learn/...-test-results/

                      If you still want to pursue X-DNA as your primary strategy, feel free, but my suggestion is that triangulation is a better choice. That is just my opinion based on my personal experiences. If you do eventually achieve success, please let us know the steps that worked for you.
                      Last edited by ech124; 17th August 2017, 02:04 PM.

                      Comment


                      • #12
                        Originally posted by ech124 View Post
                        Within the context of FTDNA, X-DNA is not treated like the other chromosomes. I don't know how ancestry.com looks at it, but they do not have a chromosome browser so that is a big disadvantage when seeking DNA proof.

                        Here is the FAQ here, so read it very carefully:


                        https://www.familytreedna.com/learn/...-test-results/

                        If you still want to pursue X-DNA as your primary strategy, feel free, but my suggestion is that triangulation is a better choice. That is just my opinion based on my personal experiences. If you do eventually achieve success, please let us know the steps that worked for you.
                        Yes, I'm very familiar with the X inheritance pattern, which I'm using in my strategy. I had consulted a FTDNA project admin on my strategy and he thought there was validity to it...(ruling out the X-matches) but that DNA acts strangely sometimes...as we can see in the ancestry.com results I posted.

                        To get back on track, I think there is validity in the my strategy, and hoping to get feedback from people who are open to the strategy, may want to test it, etc. Thanks for you input.

                        Comment


                        • #13
                          I may not be understanding what you are trying to do.

                          A distant male relative of mine shares no X-DNA with his maternal grandmother. He received his maternal grandfather's X-chromosome.

                          Using your rationale if he wasn't an X-match to your mother you would be thinking he can't be related via any line that contributed X-DNA, whereas it is quite possible the connection is via his maternal grandmother.

                          Comment


                          • #14
                            Since it is indeed possible for a person to inherit a non-recombinant X chromosome from a female (and for a sibling to inherit the other homologous X chromosome!), the lack of X matches is not strong evidence for or against a particular relationship. Rather, the existence of an X match IS evidence of a relationship that follows the pattern of inheritance of the X chromosome.

                            The lack of an X match may tip the odds, but I don't regard that as proof of anything.

                            Comment


                            • #15
                              Originally posted by ltd-jean-pull View Post
                              I may not be understanding what you are trying to do.

                              A distant male relative of mine shares no X-DNA with his maternal grandmother. He received his maternal grandfather's X-chromosome.

                              Using your rationale if he wasn't an X-match to your mother you would be thinking he can't be related via any line that contributed X-DNA, whereas it is quite possible the connection is via his maternal grandmother.
                              Two of my sisters do not match my maternal Grandfather on X, they match my maternal Grandmother along the full length of X (they received my mothers full maternal X only)

                              They show as full base pair matching along the entire X chromosome at Gedmatch when comparing them

                              So No (to alphavisions), not matching does not mean anything other then X can not be used as an aid in determining.
                              Even many of the matches at FTDNA which are deemed X matches will have a high chance of being false depending on the size of segment you are looking at (segments under 7cM)
                              Attached Files

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