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Very Small X cM for males

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  • sarahmj
    replied
    I think we need to be careful with small segments on the X, there is a good chance they may be IBS. I had a similar case with my Dad, he doesn't have many X matches, one woman matched him with a few cms on the X, but after some research it was apparent she didn't match him through his maternal line.
    I treat anything under 6cms on the X with suspicion.

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  • mabrams
    replied
    Actually it is, misleading at best.

    After I posted that original message, a light bulb went on. My mother is tested at FTDNA, although not my father.

    So I ran the 15 X matches on the In Common With filter, expecting my mother to routinely match the 15 X matches.

    My mother showed up on only 8 of the 15. Missing on seven. On some of the seven I definitely saw known paternal cousins.

    So based upon my experience, even though I do not have an X from my father, about half of my Xs are from paternal matches.

    A bit disappointing as I had hoped to use this as a phasing technique.

    I am not sure how to explain this. Often on other threads, people have cautioned about how segments on two X chromosomes can give the appearance of one longer segment. Blended, or compound segments are some of the terms I have seen. But with only one X from my mother, I think that eliminates this scenario.

    I haven't completely ruled out that my parents were related 8 to 12 generations ago. I see no places in their respective trees but their ancestral geography coincided several times. And I have several other autosomal maternal/paternal conflicts.

    I tried the tool at GedMatch for Are Your Parents Related and I got a flat zero there, but I still suspect they may be related way back when.

    That's the only way I can see how my single X maternal chromosome can contain DNA segments that seem to be more appropriately linked to my father's side.

    I am interested in your feedback, Mr W DNA and others.

    Added Later: I guess I am coming to the same conclusion as poster 192971

    Thank you
    Last edited by mabrams; 17 April 2015, 02:42 PM.

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  • 192971
    replied
    Originally posted by mabrams View Post
    Is there any chance its totally false or misleading data and the match is to my father anyway?

    I only have 15 X DNA matches at FTDNA, and 14 of those are under 7 cM and mostly under 4. So I know they are not useful for matching but can I use them for phasing to my mother's side?
    Remote X matching cannot exclude the possibility that you may be more closely related to your FF match via your father's side.

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  • dna
    replied
    Originally posted by mabrams View Post
    [----] Is there any chance its totally false or misleading data and the match is to my father anyway? [----]
    No, you have no X chromosome from your father.

    W. (Mr.)

    Leave a comment:


  • mabrams
    started a topic Very Small X cM for males

    Very Small X cM for males

    I should know this but apparently I don't. And perhaps this was discussed in another thread.

    If I have a very small amount of X DNA matching, like 1 to 3 cM, can I as a male, with only one X chromosome, at least assume its a valid phasing to my mother's side?

    I realize its IBS and I can't use it to match cousins specifically.

    Is there any chance its totally false or misleading data and the match is to my father anyway?

    I only have 15 X DNA matches at FTDNA, and 14 of those are under 7 cM and mostly under 4. So I know they are not useful for matching but can I use them for phasing to my mother's side?

    This phasing would be more useful at GedMatch, where I have 40 X DNA matches above 7cM (most are low on chr 1-22) and a full 1500 matches 3.9 cM and above.

    thanks
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