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Thread: X-chromosome inheritance patterns1626 days old

  1. #11
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    The Logic Disrupter JaM's Avatar
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    Quote Originally Posted by linkus View Post
    Since there may be some crossover between Y & X chromosomes too, I guess they felt the need to mention that it's not significant.

    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.


    Yes, that's how it is.

    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
    Interesting. Despite the great variation of crossover amounts in your chromosomes, you still end up as close to a quarter as 26.4%, which I think is fairly close.
    "A bloke walks into a pub, and asks for a pint of Adenosinetriphosphate.
    The barman says "That'll be ATP please!"

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    Women inherit exactly 0% or 50% of their X chromosmal DNA from their maternal grandmothers if no crossover is taken into consideration (not even that between two X's).

    If crossover is taken into consideration (the reality) then they inherit something between 0 and 50%. In practice it's mostly either near zero or near 50% as the crossover rate of X in humans is similar to other chromosomes which is usually a few megabases in length (of several hundred MBs) which is less than one percent of DNA exchange per generation.

    In men it's of course either 0% or 100%, and in reality usually 0-1% or 99-100%. I don't know why they talked about Y crossover because in this case it doesn't even happen as it was about maternal grandmother. Otherwise, Y crossover doesn't make significant changes in a few generations percentagewise as there are only a few hundred genes in the pseudoautosomal regions of X and Y which do recombine. Phenotypically, that can have drastic effects though.

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    double post

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    Quote Originally Posted by Jusarius View Post
    Women inherit exactly 0% or 50% of their X chromosmal DNA from their maternal grandmothers if no crossover is taken into consideration (not even that between two X's).

    If crossover is taken into consideration (the reality) then they inherit something between 0 and 50%. In practice it's mostly either near zero or near 50% as the crossover rate of X in humans is similar to other chromosomes which is usually a few megabases in length (of several hundred MBs) which is less than one percent of DNA exchange per generation.

    In men it's of course either 0% or 100%, and in reality usually 0-1% or 99-100%. I don't know why they talked about Y crossover because in this case it doesn't even happen as it was about maternal grandmother. Otherwise, Y crossover doesn't make significant changes in a few generations percentagewise as there are only a few hundred genes in the pseudoautosomal regions of X and Y which do recombine. Phenotypically, that can have drastic effects though.
    That's pretty much what I meant originally, but Linkus test result contradicts that notion. In his case large portions of the chromosomes are crossovered. That is, if his results are completely accurate, of course. That's why I would've liked to see a result for his maternal grandmother, just to see how it would correlate with the results of his grandfather.
    "A bloke walks into a pub, and asks for a pint of Adenosinetriphosphate.
    The barman says "That'll be ATP please!"

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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.
    Those estimates in these commercial ancestry tests are still only very very rough estimates. That's because I think they still don't sequence whole chromosomes. So those estimate paintings are just based on the percentage of haplotypes that match with your maternal grandfather. Also, according to that graph you inherited about 50% of your grandfather's genes assuming blue color means all of that DNA is from the same source and not just similar by chance (or inbreeding).

    ---------- Post Merged at 19:00 ----------

    So having similar regions with your grandpa doesn't mean they are all from him.

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    Quote Originally Posted by Jusarius View Post
    Women inherit exactly 0% or 50% of their X chromosmal DNA from their maternal grandmothers if no crossover is taken into consideration (not even that between two X's).
    If crossover is taken into consideration (the reality) then they inherit something between 0 and 50%. In practice it's mostly either near zero or near 50% as the crossover rate of X in humans is similar to other chromosomes which is usually a few megabases in length (of several hundred MBs) which is less than one percent of DNA exchange per generation.
    In men it's of course either 0% or 100%, and in reality usually 0-1% or 99-100%.
    No idea where you got this from but it is very far from reality. This is what a typical comparison of siblings looks like:

    http://ongenes.blogspot.com/2011/02/...-siblings.html

    If crossover rate was as insignificant as you say, siblings would only share some full chromosomes with each other rather than chunks of varying size on each chromosome.

    My case here isn't any special - ask Evon, he shares only a half of his X chromosome with his maternal grandmother too.


    Quote Originally Posted by Jusarius View Post
    Also, according to that graph you inherited about 50% of your grandfather's genes assuming blue color means all of that DNA is from the same source and not just similar by chance (or inbreeding).
    No. Look at the chart legend - light blue regions indicate half-identical segments, fully identical segments would have been marked in dark blue but there isn't a single fully identical segment between me and my grandfather which shows that he could not have been closely related to my paternal grandparents and there is no inbreeding.
    So, the fact that just over a half of my chromosomes are light blue in that chart shows that I inherited just over a quarter (NOT A HALF!) of my DNA from him.


    Quote Originally Posted by Jusarius View Post
    Those estimates in these commercial ancestry tests are still only very very rough estimates.
    Very rough estimates only concern segments that are smaller than 8cM (hence some of my telomeres seem to be inherited from nobody on the paternal side). Large segments are always shown very accurately. Look at the chart from my paternal side - there's no significant overlap between the positions of segments which I inherited from my grandmother and those that I inherited from my grandfather - I'd call such accuracy the opposite of "very very rough".
    Quote Originally Posted by linkus View Post
    Orange - paternal grandfather
    Blue - paternal grandmother

    Quote Originally Posted by JaM View Post
    That's pretty much what I meant originally, but Linkus test result contradicts that notion. In his case large portions of the chromosomes are crossovered. That is, if his results are completely accurate, of course.
    Her results. If it's not obvious enough that I'm a female from the fact that it's listed below my avatar, you might have also guessed it from the fact that I share an X chromosome with my grandmother on the paternal side.
    Last edited by linkus; 2012-10-06 at 02:09.

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    Quote Originally Posted by linkus View Post
    Her results. If it's not obvious enough that I'm a female from the fact that it's listed below my avatar, you might have also guessed it from the fact that I share an X chromosome with my grandmother on the paternal side.
    Lol, sorry about that. You're right, it should be a given.
    "A bloke walks into a pub, and asks for a pint of Adenosinetriphosphate.
    The barman says "That'll be ATP please!"

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    I have one match at 23andMe that shares 46mb with me on the X chromosome. It seems like quite a bit considering we don't share anywhere else.

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    Quote Originally Posted by Ebersdorf View Post
    I have one match at 23andMe that shares 46mb with me on the X chromosome. It seems like quite a bit considering we don't share anywhere else.
    My mother shares 47cm with her brother.I don't know if cm is the same with mb though or how the one translates to the other.
    In general sister to brother share 1/4 of brother's X(47.5cm in my case).Uncle to nephew is 1/8(23.9cm in my case).
    Sister to sister(not identical twins) is 1/2. Mother to kids 196cm that is 1/2 of mother's or the full son's X.

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    I have one on 23andme, I share 17cm on the X with her (only segment we match on).

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