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Thread: Triangulated matches and variance among family members

  1. #1
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    Triangulated matches and variance among family members

    Friends,

    I've encountered a puzzle that I haven't come across before. I've stumbled upon (I was looking at something else and came across this instead) a triangulated group of Dutch matches on my grandmother's side on MyHeritage. What's interesting about this group is that a number of my cousins (including a first and second cousin) are also involved, which helps narrow down the side of the family.

    Its a triangulated group of 7 Dutch matches (including a mother and son), and its an 8cM segment with 3584 SNPs. All of them are from the Netherlands, with numerous Dutch surnames in their trees. This is on an English branch of the family.

    The issues I have are:

    1. I match and triangulate with all 7.
    2. My grandmother matches with 5 of them, but only triangulates with 4 of them.
    3. My first and second cousins only match 1-2 of them.

    Are these possibly a bunch of false matches due to the low segment size? Or is it likely a real triangulated group, and something like SNP variance among testing companies is causing the differences?

    If someone has come across such a situation before, any input would be great.
    Ancestry on paper: English, Scottish, Irish, Welsh, Croatian, Ashkenazi, Polish and Māori.

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  3. #2
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    I have serious doubts about the reliability of Myheritage matches.
    I have lots of inconsistencies like this.

    I also have for example another inconsistency:
    I sent a phased kit from my mom, and she has matches that I don't have.
    Which is impossible since the phased kit comes from me!


    I think it's because of their imputation. Imputation involves guessing the results of untested markers from known neighboring markers.
    It is an aberration for me, but it seems that it is scientifically proven.
    But 50% of scientific research published in journals are biased and are contradicted by subsequent studies!

    Certainly that many segments are therefore probably not recognized as identical
    Last edited by Tolan; 03-27-2021 at 07:47 AM.
    Y haplogroup: R1b: L21 --> DF13 --> BY145002
    The oldest L21 known are I2457 et I2565 from Stonehenge (Beaker Culture, 2400-1900 BC)

    MTDNA: U4c1
    The oldest U4c1 known are "poz224", Yamnaya culture (2882-2698 BC), and 2 Bell-Beaker in Germany (Karsdorf, 2314-2042 BC)

    Paternal MTDNA: K1b2b
    The oldest K1b2 are Eastern European Mesolithic: Kunda Donkalnis5 (Lithuania), 6000 BC and Meso-Ene Lepenski Vir Lepe28 in Serbia, 5900 BC.
    The oldest K1b2b is Alt-3, Corded-Ware Germany (2500 BC)

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  5. #3
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    I also have some which triangulate with e.g. my grand uncle but where my own grand parent only has half of them. Because of the triangulations, I consider the matches as probably real, although likely far back in time. In some cases the segments may be close to the treshold, then slight variations in the matching locations might play a role too .

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  7. #4
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    Quote Originally Posted by Tolan View Post
    I also have for example another inconsistency:
    I sent a phased kit from my mom, and she has matches that I don't have.
    Which is impossible since the phased kit comes from me!
    I might be misunderstanding but I phased my kit against my mum's on GEDmatch. My mum shares 76.1 cM with her 5th highest match on GEDmatch. I don't match this person at all on GEDmatch. However, after I phased my kit against my mum on GEDmatch, this phased kit shares 72.9 cM with this match that I don't match with my own kit. Should that not happen?
    Ancestry: Ireland (Paper trail ≅ 81.25% Roscommon, 12.5% Galway, 6.25% Mayo)
    Y-DNA (P) ancestor (Y): Kelly b. c1830 in Co. Roscommon (Uí Maine)
    mtDNA (P) ancestor: Fleming b. c1831 in Co. Roscommon
    mtDNA (M) ancestor: McDermott b. c1814 in Co. Roscommon
    mtDNA Great grandfather: Connella b. c1798 in Co. Roscommon (T2a1a8)
    Y-DNA 2x great grandfather: Higgins b. c1816 in Co. Roscommon (R-DF109)
    Y-DNA 3x great grandfather: Fleming b. c1829 in Co. Roscommon (R-Z23534)

  8. #5
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    Quote Originally Posted by Tolan View Post
    I have serious doubts about the reliability of Myheritage matches.
    I have lots of inconsistencies like this.

    I also have for example another inconsistency:
    I sent a phased kit from my mom, and she has matches that I don't have.
    Which is impossible since the phased kit comes from me!


    I think it's because of their imputation. Imputation involves guessing the results of untested markers from known neighboring markers.
    It is an aberration for me, but it seems that it is scientifically proven.
    But 50% of scientific research published in journals are biased and are contradicted by subsequent studies!

    Certainly that many segments are therefore probably not recognized as identical
    I'm a little confused. You say, "I sent a phased kit from my mom, and she has matches that I don't have."

    I was not aware that MyHeritage has any ability to recognize a kit as having been phased, especially if you had to convert the kit into some format that could be uploaded to them. I also don't know what kind of phasing MyHeritage uses as part of its "ancestry analysis" -- if any. It's possible that the only phasing they use is statistical phasing, and in that case they would have attempted that on whatever file you sent them (already phased or not).

    In any case, your mother should have many matches you don't, since she is likely to have matches in the half of her DNA that she did not pass on to you. At any given location in her genome, she either passed on to you a segment that came from your father or a segment that came from her mother. Occasionally, a segment could be partly from one and partly from the other -- but usually only for segments which are fairly large.

    If you inherited a chunk of DNA that came from your mother's father, then you won't share a match that your mother inherited from her mother if it's in that same location. And of course the reverse is true: if the DNA you inherited from your mother at a certain location came from her mother, you won't share matches that are on your mother's father's side in that same location.

    I see this also the time with my father at 23andMe. He has matches that he may share with one or more of my siblings in a given region, but not with me; or the other way around. All that means is that my siblings and I didn't inherit the same paternal DNA at that location.
    Last edited by geebee; 03-30-2021 at 12:12 AM.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    Quote Originally Posted by FionnSneachta View Post
    I might be misunderstanding but I phased my kit against my mum's on GEDmatch. My mum shares 76.1 cM with her 5th highest match on GEDmatch. I don't match this person at all on GEDmatch. However, after I phased my kit against my mum on GEDmatch, this phased kit shares 72.9 cM with this match that I don't match with my own kit. Should that not happen?
    There is no reason you should expect to share all of your mother's matches, since she only passed on half of her DNA to you. This is even possible for a very large segment, or for several segments. I've seen instances in which full siblings share no DNA at all on a given chromosome, meaning that they inherited from opposite grandparents on both sides! This isn't common, but it happens. (You certainly would not expect it to happen at more than a chromosome or two, however.)

    The strange thing here, though, is that it really shouldn't matter whether you use a phased or unphased kit with a match this large. To be a match -- or technically, a half match -- it's only necessary that you and another person share at least one SNP value at certain sequence of SNPs. Typically, a few mismatches are allowed, though there may be limits as to how close together they're allowed to be (where both SNPs are homogenous but opposite for you and the other person). Also, depending on the algorithm, no calls may be ignored or not ignored.

    The bottom line is, phasing isn't required for matching purposes, because matching usually does take both sides into account -- and matching only has to be a single letter at each SNP location. (So for example, CG would be a half match to CT, because both have "C". GG would not be a match to TT, but a single instance in what otherwise would be a matching segment would probably be ignored.)
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    Quote Originally Posted by geebee View Post
    I've seen instances in which full siblings share no DNA at all on a given chromosome, meaning that they inherited from opposite grandparents on both sides! This isn't common, but it happens. (You certainly would not expect it to happen at more than a chromosome or two, however.)
    Me and my sister:


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  13. #8
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    Quote Originally Posted by geebee View Post
    There is no reason you should expect to share all of your mother's matches, since she only passed on half of her DNA to you. This is even possible for a very large segment, or for several segments. I've seen instances in which full siblings share no DNA at all on a given chromosome, meaning that they inherited from opposite grandparents on both sides! This isn't common, but it happens. (You certainly would not expect it to happen at more than a chromosome or two, however.)

    The strange thing here, though, is that it really shouldn't matter whether you use a phased or unphased kit with a match this large. To be a match -- or technically, a half match -- it's only necessary that you and another person share at least one SNP value at certain sequence of SNPs. Typically, a few mismatches are allowed, though there may be limits as to how close together they're allowed to be (where both SNPs are homogenous but opposite for you and the other person). Also, depending on the algorithm, no calls may be ignored or not ignored.

    The bottom line is, phasing isn't required for matching purposes, because matching usually does take both sides into account -- and matching only has to be a single letter at each SNP location. (So for example, CG would be a half match to CT, because both have "C". GG would not be a match to TT, but a single instance in what otherwise would be a matching segment would probably be ignored.)
    I understand that, of course, my mum will have matches that I don't have. I was just wondering does it make sense that I can match someone after phasing with a parent if I don't match them at all with my regular non-phased kit? If that does make sense and is unsurprising, then that's fine.
    Ancestry: Ireland (Paper trail ≅ 81.25% Roscommon, 12.5% Galway, 6.25% Mayo)
    Y-DNA (P) ancestor (Y): Kelly b. c1830 in Co. Roscommon (Uí Maine)
    mtDNA (P) ancestor: Fleming b. c1831 in Co. Roscommon
    mtDNA (M) ancestor: McDermott b. c1814 in Co. Roscommon
    mtDNA Great grandfather: Connella b. c1798 in Co. Roscommon (T2a1a8)
    Y-DNA 2x great grandfather: Higgins b. c1816 in Co. Roscommon (R-DF109)
    Y-DNA 3x great grandfather: Fleming b. c1829 in Co. Roscommon (R-Z23534)

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    Quote Originally Posted by peloponnesian View Post
    Me and my sister:
    Thanks, I am surprised at the extreme results.

    I am curious which test and version that you two used?

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    Quote Originally Posted by C J Wyatt III View Post
    Thanks, I am surprised at the extreme results.

    I am curious which test and version that you two used?
    It's from the latest MyHeritage chip uploaded to Gedmatch. I wonder how it would look if we both did whole genome testing.

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