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Thread: X Match Question

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    X Match Question

    On my GEDmatch matches there is only one person among my 1,500 matches who is an X match AND a match proper: my half-sister. I share some X chromosome matches with a few others, the largest of them being 24 cM. However, when I check the one-to-one autosomal comparison utility on those X matches using 7cm/700SNPS, I do not match ANY of them.

    Is this unusual?

    Thank you.

    Wolfie

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     Smilelover (10-22-2016)

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    No more unusual than matching on just one autosomal chromosome.

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     Wolfie (09-15-2014)

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    Dear Wolfie,
    Because of your post I got curious on X match lengths. Out of curiousity I checked my various kits. Someone matches my mom for 22.51 cM (excluding me). For me, (excluding mom) the largest match was 17 cM. For my uncle, his largest -X- match was for 16cM.
    dp :-)

    Quote Originally Posted by Wolfie View Post
    On my GEDmatch matches there is only one person among my 1,500 matches who is an X match AND a match proper: my half-sister. I share some X chromosome matches with a few others, the largest of them being 24 cM. However, when I check the one-to-one autosomal comparison utility on those X matches using 7cm/700SNPS, I do not match ANY of them.

    Is this unusual?

    Thank you.

    Wolfie
    Grace and good eure and long prosperitee. [Lydg. Mum. Goldsmiths]

    ysearch/mitosearch id: atr94 GENBANK/ENA mtDNA id: KF703542 member ISOGG

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     Wolfie (09-15-2014)

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    Grace and good eure and long prosperitee. [Lydg. Mum. Goldsmiths]

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     Wolfie (09-15-2014)

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    GEDmatch (in red letters) says that you should use the 7cM/700SNP comparison, and that if there is no match, then you should not contact the person. What would that mean regarding my X matches, whom I do not match otherwise?

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    Quote Originally Posted by Wolfie View Post
    GEDmatch (in red letters) says that you should use the 7cM/700SNP comparison, and that if there is no match, then you should not contact the person. What would that mean regarding my X matches, whom I do not match otherwise?
    GEDMATCH:
    To qualify as a 'match' in the genealogical time frame, results must have a largest Autosomal segment that has at least 700 SNPs and be at least 7 cM.
    It must have BOTH. Results with the largest segment less than 7 cM are highlighted in pink.
    In general, the results shown below use thresholds LESS than 7cm / 700 SNPs.
    PLEASE verify any result shown on this list with the one-to-one comparison tool before assuming any match is real.
    To check the number of SNPs, click on the 'A' on the same line to view the one-to-one comparison detail.

    DP:
    X & Y are allosomes. For your particular question, for segment length, I'm not sure.
    Last edited by dp; 09-15-2014 at 09:33 PM.
    Grace and good eure and long prosperitee. [Lydg. Mum. Goldsmiths]

    ysearch/mitosearch id: atr94 GENBANK/ENA mtDNA id: KF703542 member ISOGG

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     Wolfie (09-15-2014)

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    Quote Originally Posted by Ann Turner View Post
    No more unusual than matching on just one autosomal chromosome.
    is "Going Through a Phase: Haplotyping the Female X Chromosomes" a paper written by you perhaps.
    dp :-)
    Grace and good eure and long prosperitee. [Lydg. Mum. Goldsmiths]

    ysearch/mitosearch id: atr94 GENBANK/ENA mtDNA id: KF703542 member ISOGG

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    Quote Originally Posted by David Powell View Post
    GEDMATCH:
    To qualify as a 'match' in the genealogical time frame, results must have a largest Autosomal segment that has at least 700 SNPs and be at least 7 cM.
    It must have BOTH. Results with the largest segment less than 7 cM are highlighted in pink.
    In general, the results shown below use thresholds LESS than 7cm / 700 SNPs.
    PLEASE verify any result shown on this list with the one-to-one comparison tool before assuming any match is real.
    To check the number of SNPs, click on the 'A' on the same line to view the one-to-one comparison detail.

    DP:
    X & Y are allosomes. For your particular question, for segment length, I'm not sure.
    In practice what you say is true for Family Tree DNA, but that's because they have never computed matches based on the X chromosome. They just display any X segments that are present in matches they've already computed, based on the autosomes. The vast majority of the X segments you see at FTDNA will be pseudo-segments.

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    Thank you, Ann. I just read your article, mentioned here by David Powell. I am trying to understand this mysterious science. Before embarking on the journey to find my biological father (July 18, 2014), I had absolutely no knowledge of this sort of thing, save a tiny bit gleaned from a class in high school eons ago. I have a question for you. Is it true that full-sisters ALWAYS match the entire X? Are there ever exceptions?

    Wolfie

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    Quote Originally Posted by Wolfie View Post
    Thank you, Ann. I just read your article, mentioned here by David Powell. I am trying to understand this mysterious science. Before embarking on the journey to find my biological father (July 18, 2014), I had absolutely no knowledge of this sort of thing, save a tiny bit gleaned from a class in high school eons ago. I have a question for you. Is it true that full-sisters ALWAYS match the entire X? Are there ever exceptions?

    Wolfie
    The exceptions are rather minor, and perhaps theoretical. The very tips of the X chromosome do exchange DNA with the very tips of the Y chromosome, and the exact points of exchange could differ with each conception. Or a mutation could occur during the creation of different sperm (but the mutation rate is exceedingly low). But basically, full sisters will be at least half-identical as far as we can tell with our current testing procedures.

    Full sisters will also (usually) be completely identical for portions of the X. The mother recombines her two X chromosomes when creating an egg. In some regions her daughters will get the same stuff and in other regions they will get different stuff.

    The animations at this website give a good overview of the different patterns of inheritance.

    http://www.smgf.org/pages/animations.jspx

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