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  • prairielad
    replied
    FTDNA does not test the PAR regions (might on new chip) but does not use these regions for matching. PAR are areas at the beginning and end of X and Y which CAN (not always) recombine.
    So it does not effect X matching.
    Regions are so small I would doubt they would show up anyways, under 5cM if that

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  • snetphilie
    replied
    One thing nobody ever seems to mention is the fact that part of the X chromosome recombines with the Y Chromosome.

    So it is in fact possible for you to inherit part of your X chromosome from your mother's father's father. Your mother's father's X partially recombined with his Y, so one of your mother's X's contains a portion of her father's Y, and then her two X's recombine and you likely get some of that passed onto you.

    The same holds true for your father. Part of his X and Y recombined, so if you are male, you received part of the X he got from his mother in your Y chromosome, and of course the rest of the Y from him, but even his Y was a combination of his father's X and Y. If you are female, you still receive part of the Y that your father got from his father.

    Moral of the story is, the X match doesn't filter out the part of the X that recombines with the Y, so it is not a very accurate indicator of anything.

    Oh, and here's a video that shows how the X/Y recombination is different than the other chromosomes! https://www.biointeractive.org/class...n-y-chromosome

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  • mabrams
    replied
    I am very glad that FTDNA has included the X DNA.

    But their format is very flawed. An Opinion.

    a. Men in general, have far fewer X matches to start with. The column is basically wasted space. Even for women the column has little obvious use

    b. FTDNA has the awkward protocol of announcing any X DNA match coupled with an autosomal match, regardless of how small. And most are very small. << 7 cM. Many are psuedo-segments. You can't see them on the chromosome browser unless you turn it down to 1 cM.

    c. Just stating "X-Match" is almost pointless. Why not the cM numbers? Imagine if the Shared or Longest columns just said "A-Match" This does not seem like a major programming challenge.

    d. The X-Match column does not sort correctly. When I sort it, I do get the X-matches bunched to the top. But they are not sorted by the cM amount, which is what I think what was implied by sorting with an up and down "arrow".

    e. Like Matt said, if a person has a large X match but no autosomal match, then you won't see them. I have a 4th cousin with 54 cM of X but a low amt of autosomal so she is just not a match at all.

    I think my concerns would be somewhat obviated if they just displayed the cM and I could see if the cM was like 15 or 1.
    And fixed the sorting.

    I would at least consider including matches that are solely on the X, and maybe replace the Relationship range with a cautionary note. Perhaps with higher thresholds.

    So its nice that FTDNA does include the X data, but the presentation is often misleading. GedMatch has a much more efficient approach.

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  • MoberlyDrake
    replied
    Looking at my mother's X matches, I find that most of them share segments with her that are under 5 cM. Most seem to be of UK ancestry, and all her true X chromosome matches would have to have French or German ancestry, because only her father's father has British ancestry.

    I think I would ignore segments under 5 cM, maybe under 7 cM. I heard somewhere that for the X chromosome, you should ignore segments under 10 cM, but I don't know about that.

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  • mkdexter
    replied
    Originally posted by Germanica View Post
    Be aware that there is less recombination on the X chromosome because fewer ancestors are contributing to it. This can make it seem like a match is a closer match than they are, but this is why (I believe) X-DNA isn't used in the total amount of shared DNA for calculating estimated relationships, and why (again, I think) they don't report matches who ONLY share X-DNA and no other DNA on any other chromosome.
    To the first point I'm not sure what you meant by less recombination. I could guess.. but anyway sometimes the x recombines and sometimes it copies, the non-par loci areas that is.

    When the X matching first became part of the FTDNA test they did not report just shared X, so you did have to have an autosomal match first and correct the total shared does not include the X share of about 196cM.
    Last edited by mkdexter; 22nd September 2016, 03:02 AM.

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  • Germanica
    replied
    Originally posted by william dimon View Post
    What is the significance of an x in the x match column on your match lists?
    I'm not sure what you mean by "an x in the x match column". My X Match column either says "X-Match", which means that person and I share DNA on the X chromosome, or it's blank. There are none that just have "an x".

    If you're asking what the significance of sharing DNA on the X chromosome is, it limits the possible ancestors you might share with that person. Women get two X chromosomes, one from their father, and one from their mother. Men get one X chromosome, from their mother. So X-DNA can not pass through two or more males in a row. Since you are male, that means all your X matches are on your mother's side. The lack of shared X DNA does not necessarily mean the match is on your father's side though - they can still be on your mother's side but you just didn't happen to inherit any shared DNA on the X chromosome.

    I did not expect this images to display so large so I'm just going to post links: http://3.bp.blogspot.com/-bzSdU-ZJpB...ine+300dpi.tif

    http://4.bp.blogspot.com/-zeudaGTif3...ine+300dpi.tif

    These charts show which branches your X-DNA comes from if you are male or female.

    Be aware that there is less recombination on the X chromosome because fewer ancestors are contributing to it. This can make it seem like a match is a closer match than they are, but this is why (I believe) X-DNA isn't used in the total amount of shared DNA for calculating estimated relationships, and why (again, I think) they don't report matches who ONLY share X-DNA and no other DNA on any other chromosome.

    Leave a comment:


  • william dimon
    started a topic x match

    x match

    What is the significance of an x in the x match column on your match lists?
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