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Verifying Matches- Phasing and Triangulate

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  • Verifying Matches- Phasing and Triangulate

    Taken from a different topic, but does anyone mind to explain how to “phase and triangulate” to verify matches?

    “I also need to remind everyone that about 5% of our matches in Family Finder are outright false. They should be phased and triangulated to be sure they are real matches.”

    I appreciate anyone who can help me with learning as I am really fascinated by genetics and genealogy and would like some trusted tools for research .

  • #2
    I'm pretty sure I already talked about this elsewhere on this forum in past years, but in any event you can find the details you need at Jim Bartlett's blog Segmentology.org

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    • #3
      Where is that quote from, Melissa122? Another forum post?

      For triangulation, Roberta Estes has more than a few articles on it.

      For phasing, there is the Family Matching system at FTDNA, and Roberta's posts about phasing. Beyond those, there is an advanced method called Visual Phasing, which is not something I would recommend for someone who is new to DNA for genealogy to try. It is a lot of work, and I've only dipped my toe in it in the past. If you're interested in getting an idea of what's involved with Visual Phasing, Blaine Bettinger has a five-part Series on it at his "The Genetic Genealogist" blog:You would probably be much better off using DNA Painter as a tool to map your chromosomes, or the Leeds Method to help sort your matches, as alternatives to Visual Phasing.
      Last edited by KATM; 5 June 2020, 12:01 PM.

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      • #4
        The false positive rate at FTDNA is well over 5%.

        Roberta Estes phases DNA data from a child and both parents and gives percentage of false positives for the child by segment size.

        https://dna-explained.com/2017/01/19...false-matches/

        The false positive rate for 11 to 11.99 cM is 5% and quickly increases to 54% for 7 to 7.99 cM.

        You have to be very careful with triangulation as both IBD and IBP segments will triangulate. IBP matches are not false matches (IBC), but the shared DNA is from too far back to determine the MRCA.

        I am cursed with hundreds of IBP matches on multiple chromosomes on my Irish ancestry. One of the IBP areas consists of shared 20 cM segments.

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        • #5
          khazaria - I will look for your previous posts, if they are anything like your other posts then I know they will be super helpful and in depth. It is Appreciated.

          @KATM-Thanks again ! This is perfect, and sorry this is from a different topic so I wasn't sure if I should ask in the thread, or start a new one. So much for my forum etiquette!
          I know I could just google these terms, but you folks know the little nuances and trends with this stuff, this forum has been untapped wealth of info for someone just getting started.

          jimbirk Thanks for the heads up. How do you isolate IBP segments, or is it easily identifiable? Will I know it when I see it ? /sorry if this is a should know question.

          Thanks Again!

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          • #6
            Originally posted by jimbirk View Post
            You have to be very careful with triangulation as both IBD and IBP segments will triangulate. IBP matches are not false matches (IBC), but the shared DNA is from too far back to determine the MRCA.
            That's not what she was trying to accomplish in the other thread. She was trying to figure out whether she had a Jewish ancestor or not, or whether those Jews have a Slavic ancestor. Both possibilities exist. Due to the timeframes involved here, and the general lack of Jewish records pre-1800, a population match on a triangulated segment would be a reasonable expectation but finding the name of a common ancestor through a paper trail would be nearly impossible.

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            • #7
              Originally posted by khazaria View Post

              That's not what she was trying to accomplish in the other thread. She was trying to figure out whether she had a Jewish ancestor or not, or whether those Jews have a Slavic ancestor. Both possibilities exist. Due to the timeframes involved here, and the general lack of Jewish records pre-1800, a population match on a triangulated segment would be a reasonable expectation but finding the name of a common ancestor through a paper trail would be nearly impossible.
              Thank you for clarifying and explaining my intentions ! Us newbies can be a pain in the ... lol

              Sorry guys I didn’t provide better context, but Khazaria summed it up correctly.
              Last edited by Melissa122; 6 June 2020, 09:02 AM.

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              • #8
                Originally posted by khazaria View Post

                That's not what she was trying to accomplish in the other thread. She was trying to figure out whether she had a Jewish ancestor or not, or whether those Jews have a Slavic ancestor. Both possibilities exist. Due to the timeframes involved here, and the general lack of Jewish records pre-1800, a population match on a triangulated segment would be a reasonable expectation but finding the name of a common ancestor through a paper trail would be nearly impossible.
                khazaria. Would this 7% mix of West Asian combined with the Ukrainian/polish be a clue as to a more ancient Jewish relation ? Sorry to chase you down with questions you probably answered 100 times, but it was something that stuck out as a possible clue? (however I am assuming this not coming from my MTDNA (non jewish HG - H1ag) as we talked about previously. I don't want to make strained assumptions, but you are obviously very knowledgeable about Jewish and admixtures/other ethnic groups. If I am serving up useless information, feel free to say so lol.

                Eurogenes EUtest V2 K15 Admixture Proportions


                k15 ged.PNG

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                • #9
                  I wanted to update what I have found and hopefully someone can make some sense of it. I have 2 things going on. This focus is on my maternal (mtdna which is my English-German) side and my maternal-paternal (mother's father) which is my Polish/Ukrainian side. I cant confirm where the autosomal Jewish matches are coming from. Here is what I have

                  MTDNA
                  HRV-1 = about 200 Ashkenazi. Sephardic, and Mizrachi matches
                  HRV-2 = (about 40 total) 6 listed as Mizrachi
                  Coding region = about 1/4 with a Jewish surname ( I know some names are just German and not Ashkenazi per say but one example is Kohlmann)

                  AUTOSOMAL - 1/4 with Jewish surnames ( ex: Kaplan, Bloom, Kulewicz)
                  With this particular mehl it lists him as a closer relative (The tree he is in is of a Jewish Family)
                  mehl.PNG
                  I did a 1;1 with this particular Kaplan and longest seg was 13.5 (said about 4.5 generations to CA
                  I also did a 1:1 with a match with someone that had K1a1b1a, but that longest seg was 10.5 with 29.5 half segs.

                  We also found a big discrepancy with my Grandmother's father. We were always told my great grandfather had the surname Reynolds (English), but her Birth cert says "Wehner". I know that is not a Jewish surname, but it is German, so I am wondering if that matches are tying in to my German side. Lastly, although I hesitate to bring this up because you can't go by phenotype, but I used to work for a well known Jewish Family Business in my city. It was located in our City's Jewish community. I was one of 3 people working there who was not Jewish. (90% of our customer base was also Jewish). Everyone that worked there and customers either commented that I must have Jewish ancestry, or thought I was new to the community. ( I know Ashkenazi can be blonde and blue eyed, but they were referring to the more middle eastern look I have).

                  I know I have brought similar questions up recently and I do not want to be grasping at genetic "noise" if that is all this is. Just hoping someone can tell me what the match quality means and if number of matches tells me anything, or points is one direction or another (Jewish Ancestry or no Jewish Ancestry). I really want to be able to pass our history on to my Daughter whatever the truth may be.

                  Thanks for reading and being understanding as I muddle through learning all this.

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                  • #10
                    Like I said, your mtDNA is not a Jewish line. HVR1-only matches are too far away to be meaningful. Kohlmann with 2 n's is unlikely to be Ashkenazic. Most Ashkenazic surnames have only 1 n. Most German Christians have 2 n's.
                    There are occasionally autosomal DNA connections between German Christians and German Jews which can show up in Family Finder and most of the time it's from a shared Jewish ancestor. With the downgrading of GEDmatch's interface, I really can't do a full search and analysis for you like I could before last June. Sorry. Maybe there are some matches that are valid and which would triangulate but it'll be hard to prove. You should download your complete Chromosome Browser file and look for patterns on the longest segments. If you found a segment where there are multiple Ashkenazim sharing the same segment region on the same chromosome number, you might be getting somewhere.

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                    • #11
                      Thanks for an option to explore, I will do that. I assume to look for longest segments in the same location and I am an analyst so if there are patterns, I hope I would see them lol. If not then I can take that as some sort of answer. Thanks Again!

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                      • #12
                        Originally posted by khazaria View Post
                        Like I said, your mtDNA is not a Jewish line. HVR1-only matches are too far away to be meaningful. Kohlmann with 2 n's is unlikely to be Ashkenazic. Most Ashkenazic surnames have only 1 n. Most German Christians have 2 n's.
                        There are occasionally autosomal DNA connections between German Christians and German Jews which can show up in Family Finder and most of the time it's from a shared Jewish ancestor. With the downgrading of GEDmatch's interface, I really can't do a full search and analysis for you like I could before last June. Sorry. Maybe there are some matches that are valid and which would triangulate but it'll be hard to prove. You should download your complete Chromosome Browser file and look for patterns on the longest segments. If you found a segment where there are multiple Ashkenazim sharing the same segment region on the same chromosome number, you might be getting somewhere.
                        Thanks for the direction. I just DL d the file. I did read about what you said about the HG, but I just wanted to list what I had in case it was relevant. I do really appreciate the offer for additional research and it’s a bummer ged match changed !
                        The only issue is some of these matches are my heritage, geni, and ged match matches. Ft is only one database, but it sounds like a solid starting point as I read good things about FT’s matching system. In the end, even if I don’t see anything significant to any Ashkenazim, it will still be a way to organize and see clusters. Good starting point for a noob ☺️
                        Last edited by Melissa122; 9 June 2020, 06:59 PM.

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                        • #13
                          So I took khazaria s advice and DL my matches. It wasn’t hard to find clusters of matches ( in general) but that was as far as I got on the spreadsheet. I had a lot less matches in ged match in general so I looked at those. I’m only getting started so here is my question if someone can help. I’m using this as an example so maybe someone can explain the significance if any on this :

                          On GED I am finding a pattern of matching on chromosome 20 between 58-60. When I start to see something like this , what exactly is it telling me ? Do my need to match on multiple chromosomes that all match up to be significant ? Just trying to get some context as I do this so I know what to ignore and what to flag. Thanks !

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