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Thread: X-chromosome inheritance patterns1619 days old

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    Default X-chromosome inheritance patterns

    If you have found cousins at your X at 23andme, then this should be interesting to know. I'm not an expert, I'm assuming this is right. Could anyone confirm it please?

    The chart for a woman's X DNA inheritance shows that she inherits 25% (0%-50%) of her X DNA from her maternal grandmother. This means that on the average, a woman inherits 25% of her X DNA from her maternal grandmother, but could inherit as little as 0% or as much as 50%. The chart also shows that a woman inherits 50% (50%) of her X DNA from her paternal grandmother. This means that a woman inherits exactly 50% of her X DNA from her paternal grandmother. These charts ignore the possibility of Y crossover, which doesn't seem to contribute significantly to X chromosomes.
    http://freepages.genealogy.rootsweb....heritance.html

    X chromosome inheritance for a woman:

    5 generations chart:
    http://freepages.genealogy.rootsweb....%205%20gen.pdf

    6 generations chart:
    http://freepages.genealogy.rootsweb....%206%20gen.pdf

    X chromosome inheritance for a man:

    5 generations chart:
    http://freepages.genealogy.rootsweb....%205%20gen.pdf

    6 generations chart:
    http://freepages.genealogy.rootsweb....%206%20gen.pdf
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    Do you mean cousins, or do you mean "cousins"? I have a ~9cm "cousin" match on the x chromosome-he's my only one.

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    I meant 23andme cousins. Knowing the inheritance pattterns can help us track the cousins we find at the X.
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    As little as 0%?

    I don't know about cousins, but my daughters surely resemble their paternal grandmother more than anyone else in the family-- down to eye color and hair color/ texture.

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    edit: I misread the last part!

    Quote Originally Posted by larali View Post
    As little as 0%?

    I don't know about cousins, but my daughters surely resemble their paternal grandmother more than anyone else in the family-- down to eye color and hair color/ texture.
    It's only about the X-chromosome. Your daughters looks aren't determined just by the X-chromosome.
    Last edited by JaM; 2012-10-05 at 03:56.
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    Quote Originally Posted by JaM View Post
    The text in the quote is not correct. When the text says "X DNA" it really talks about a chromosome pair. You cannot inherit partial chromosomes. You always inherit exactly ONE chromosome (there are two X chromosomes in a pair) never a half chromosome. So you inherit either 50% (IE one chromosome) or 0% (no chromosome) excluding crossover, from a grandparent. On the maternal line it comes either from the grandfather or the grandmother, while on the paternal line it always comes from the grandmother. There's no such thing as a 25% inheritance of a X chromosome pair.
    Might I ask you why are you excluding crossover?

    Me vs my maternal grandfather:


    There clearly is such thing as inheriting 25% of one's chromosome pair from some particular grandparent.
    Last edited by linkus; 2012-10-05 at 03:48.

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    Quote Originally Posted by linkus View Post
    Might I ask you why are you excluding crossover?

    Me vs my maternal grandfather:


    There clearly is such thing as inheriting 25% of one's chromosome pair from some particular grandparent.
    Sorry, I happened to have misread the text, since I believed it excluded the crossover, but it only talked about Y crossover (which should be fairly irrelevant on the maternal line anyway)

    So, what percentage of match do you have with your two maternal grandparents? I haven't done any kind of research about this, but I could imagine some kind of difference in the parts which would be crossovered or not. I would imagine that the percentages aren't 25%25%. I don't quite get the meaning of the chart, though. I presume that every chromosome represents a pair?

    Here's a quick and dirty representation as I see it, the X from your chart, is that how it's supposed to be read?



    Black=maternal grandfather

    According to your chart, chromosome (pair?) 20 has no crossover whatsoever - or the chromosomes are just randomly matching between your grandparents in the crossover parts. Do you have the results for both your grandparents, or just your maternal grandfather?
    Last edited by JaM; 2012-10-05 at 04:27.
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    Quote Originally Posted by JaM View Post
    Sorry, I happened to have misread the text, since I believed it excluded the crossover, but it only talked about Y crossover (which should be fairly irrelevant on the maternal line anyway)
    Since there may be some crossover between Y & X chromosomes too, I guess they felt the need to mention that it's not significant.

    Quote Originally Posted by JaM View Post
    So, what percentage of match do you have with your two maternal grandparents? I haven't done any kind of research about this, but I could imagine some kind of difference in the parts which would be crossovered or not. I would imagine that the percentages aren't 25%25%.
    True. The inheritance is rarely that tidy - the exact percentage for each chromosome isn't given but in total I inherited 26.4% of my DNA from my maternal grandfather.


    Quote Originally Posted by JaM View Post
    I don't quite get the meaning of the chart, though. I presume that every chromosome represents a pair?
    Here's a quick and dirty representation as I see it, the X from your chart, is that how it's supposed to be read?



    Black=maternal grandfather
    Yes, that's how it is.

    Quote Originally Posted by JaM View Post
    According to your chart, chromosome (pair?) 20 has no crossover whatsoever - or the chromosomes are just randomly matching between your grandparents in the crossover parts. Do you have the results for both your grandparents, or just your maternal grandfather?
    I only have the results of grandmother's brother on my maternal side.
    Orange - maternal grandmother's brother
    Blue - maternal grandfather





    But I have the results of both of my grandparents on the paternal side. 23andme's charts don't seem to be very random but they're not perfect either. Some of my telomeres seem to have been inherited from nobody..
    As you can see, the recombination rate was quite a bit lower on the paternal side (on average recombination rate is 1.7 times higher among females than males and it's also higher in young females, so it's no surprise).

    Orange - paternal grandfather
    Blue - paternal grandmother
    Last edited by linkus; 2012-10-05 at 06:33.

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    Quote Originally Posted by larali View Post
    As little as 0%?

    I don't know about cousins, but my daughters surely resemble their paternal grandmother more than anyone else in the family-- down to eye color and hair color/ texture.
    I may have mentioned before that we have a 2.8 cM X match on Gedmatch in addition to the 7.3 cM match that also shows up on 23andMe. This means I am somehow related to you through my maternal grandfather, which I had already concluded by how the autosomal segment came back strongly Eastern Euro, since that's the only known source I have for such ancestry.

    Anyway with such a distant match on that particular ancestry, it probably dates back to a common ancestor 300-500 years ago somewhere like Poland, meaning we'll never find it. I have a match on that same line, a genealogy confirmed 3rd cousin once removed, with a common great grandfather born in 1844, immigrated from Germany, born in Prussia. He matches me on 4 segments for a total of 79 cM, my largest accepted Relative Finder match. You don't match him at all, wtf? That probably narrows it down to a smaller set of my Polish and west Prussian immigrant ancestors but they don't match any of your surnames.

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    Thanks for the charts. Pretty much all of my Ashkenazi/European ancestry is concentrated on the X.

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