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Inheritance of the X gene?

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  • Inheritance of the X gene?

    A male's X is simple enough - his mother.
    And so is a female's - her mother, her father's mother.

    That is the most basic summary.

    However, WHICH X is the daughter inheriting from her mother?

    Her mother's mother's X? Her mother's father's mother X? A combination of the two?

    Is it simple like this?
    http://s30.postimg.org/5fuzn45tt/image.png

    Or is it complex like this?
    http://s9.postimg.org/3sglrfcq7/image.png

  • #2
    X chromosome, not "X gene". X chromosome contains many genes.

    X from father to daughter is inherited as such, but the inherited X chromosome from mother to son or daughter is almost always a mixup of the two X chromosomes of mother.

    http://dna-explained.com/2012/09/27/x-marks-the-spot/

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    • #3
      Originally posted by 192971 View Post
      X chromosome, not "X gene". X chromosome contains many genes.

      X from father to daughter is inherited as such, but the inherited X chromosome from mother to son or daughter is almost always a mixup of the two X chromosomes of mother.

      http://dna-explained.com/2012/09/27/x-marks-the-spot/
      You are aware that genes are on chromosomes right? To complain is like complaining of tomato vs. tomatoe.

      As it is, this is as I thought it was.

      So the X is a mixture. To say that the X from the male is inherited "just like that" as it 100% pure is actually erroneous because the male would have inherited the mixed up X from his mother - which itself would be a combination of the X from her mother and her father's mother.

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      • #4
        Originally posted by Ashley87 View Post
        To say that the X from the male is inherited "just like that" as it 100% pure is actually erroneous because the male would have inherited the mixed up X from his mother - which itself would be a combination of the X from her mother and her father's mother.
        Well you got the recursive X inheritance pattern right. In any case, males are never "guilty" of mixing up (or better said, recombination) of the X chromosome genetic material, because they cannot be.

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        • #5
          Originally posted by 192971 View Post

          X from father to daughter is inherited as such, but the inherited X chromosome from mother to son or daughter is almost always a mixup of the two X chromosomes of mother.
          To say that the x a mother passes on to her children is "almost always a mixup of the two X chromosomes of mother" is a bit of an overstatement. There are cases where a mother will pass on the x she received from one of her parents intact, without any recombination. It's certainly not close to half the time, but it's more common than is generally thought.

          One experienced genetic genealogist has several relatives from three generations tested and has found in these cases that an unrecombined x is passed on by a female relative to her child about 25% of the time. That's anecdotal, but I think it's not an isolated case with one family's testing. According to this article at http://www.genie1.com.au/blog/63-x-dna:

          "A mother contributes an X chromosome that is usually a recombined mix of both of her X chromosomes (but not always), and fathers contribute their whole X chromosome intact to their daughters.

          "If half sisters with the same mother share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X."

          The bolding is mine for emphasis.

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          • #6
            Originally posted by MMaddi View Post
            To say that the x a mother passes on to her children is "almost always a mixup of the two X chromosomes of mother" is a bit of an overstatement.
            OK, well, maybe. I did not remember what the estimate of probability of inheriting of non-recombined X chromosome from mother was. However, I think that the anecdotal case does not necessarily a proper statistic make. It may even be possible that some X chromosome strains are more resistant to recombination than others - who knows?

            Should we now discuss also how Y chromosome may recombine with X chromosome within the small pseudoautosomal regions? I forgot to mention that, too. So, what I told: "males are never 'guilty' of mixing up (or better said, recombination) of the X chromosome genetic material, because they cannot be." was also a bit of an overstatement.

            Well, all this just emphasizes what I have told myself: "Genetics is not as simple as you think it is." But generally going right away into exceptions of the main principles is rarely the best way to learn new things.

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            • #7
              The X chromosome female recombination rate is generally stated as 194.6 cM. By definition there will statistically be a recombination/crossover 1946 times for every 1000 events (female births). These are Rutgers data, not mine, at http://compgen4.rutgers.edu/RutgersMap/MapBrowser.aspx

              For males there is X-Y recombination as well at the very extreme ends (only 35.9cM). This X-Y mixing is too small and unpredictable and is generally ignored totally by the as-DNA testers/chips.

              There is surely more detail on this and I am a mere hobbyist, so more worthy experts may chime in.

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              • #8
                Originally posted by hansonrf View Post
                The X chromosome female recombination rate is generally stated as 194.6 cM. By definition there will statistically be a recombination/crossover 1946 times for every 1000 events (female births). These are Rutgers data, not mine, at http://compgen4.rutgers.edu/RutgersMap/MapBrowser.aspx

                For males there is X-Y recombination as well at the very extreme ends (only 35.9cM). This X-Y mixing is too small and unpredictable and is generally ignored totally by the as-DNA testers/chips.

                There is surely more detail on this and I am a mere hobbyist, so more worthy experts may chime in.
                1. Assuming that some freakishly high volume of X-Y recombination must occur in some isolated individuals, would it likely result in unviability or severe deformity?

                2. And vis-à-vis Y chromosome STR analysis, would it more likely result in a massive number of loci returning null readings or could it result in merely unusual STR counts at individual loci?

                3. I find the whole the topic of recombination on the X chromosome so completely baffling that I can't imagine any useful rule of thumb for interpreting autosomal matches there.

                Comment


                • #9
                  Originally posted by hansonrf View Post
                  The X chromosome female recombination rate is generally stated as 194.6 cM. By definition there will statistically be a recombination/crossover 1946 times for every 1000 events (female births). These are Rutgers data, not mine, at http://compgen4.rutgers.edu/RutgersMap/MapBrowser.aspx
                  That statement is making me feel really stupid. Can anyone help explain what that means?

                  Appreciate it!

                  Jack

                  Comment


                  • #10
                    Originally posted by Frederator View Post
                    1. Assuming that some freakishly high volume of X-Y recombination must occur in some isolated individuals, would it likely result in unviability or severe deformity?
                    No, because like in autosomes the exhanged regions are homologous, ie. the same except random (point) mutations. There is, of course, a strong selection pressure against Y chromosome losing its main function: making a male chromosomal child a fertile male.

                    Originally posted by Frederator View Post
                    2. And vis-à-vis Y chromosome STR analysis, would it more likely result in a massive number of loci returning null readings or could it result in merely unusual STR counts at individual loci?
                    Like hansorf told the pseudoautosomal regions of Y chromosome are ignored, that is, excluded from STR analysis. No readings from there. (Could be fun if there would be a test spesifically for the pseudoautosomal regions of Y. Very baffling *paternal side* matches for males!)

                    Originally posted by Frederator View Post
                    3. I find the whole the topic of recombination on the X chromosome so completely baffling that I can't imagine any useful rule of thumb for interpreting autosomal matches there.
                    I understand. This is not like a rule of thumb, but:
                    "When normal X inheritance is assumed (ie. no uniparental disomy of X happening), and you are a male and you have an autosomal match who you share also an X chromosomal segment (IBD, non-IBS is without other information only certain for male-male X match pairs), then the match must be related to you via your X relatedness allowing maternal side ancestors, unless the match is your daughter or an X inheritance allowing offspring of your daughter. Still, in general, X relatedness cannot exclude remote relatedness to your autosomal match also via your paternal side."
                    The rest is not as clear as that.

                    Comment


                    • #11
                      georgian1950, what hansdorf said about recombination rate of X chromosome, means simply that in average an X chromosome is cut at two locations (194.6/100 = 1.946 ~= 2) when an egg cell is formed.

                      Take two different colored strings (say green and red) side by side and cut them both twice at the same locations and switch both the end parts to their opposite color counterparts, so that you then have green-red-green line and red-green-red line "chromosomes". That "simulates" two crossovers or two recombination events. Only one of those mixed color lines goes to an egg cell, which has only one X chromosome. The egg cell may then go ahead an receive an X or Y containing sperm.

                      In reality sometimes the X chromosome is not cut at all, sometimes cut once, sometimes twice and sometimes even more times when an egg cell is formed. The autosomal chromosomes behave similarly to X in egg cell formation, but recombine also when sperm cells form. Each autosome have its own recombination rate (positively correlated to its length in bases).

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                      • #12
                        Originally posted by 192971 View Post
                        georgian1950, what hansdorf said about recombination rate of X chromosome, means simply that in average an X chromosome is cut at two locations (194.6/100 = 1.946 ~= 2) when an egg cell is formed.
                        Thanks, I think I understand the recombination, but I am having trouble with how the rate is expressed.

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                        • #13
                          Following attachments are of my Families X inheritance based on manually phasing our Raw Data files. Also shows the FTDNA chromosome browser shared sections between each of us (my sisters share is based on Gedmatch phased maternal data, as FTDNA show them as full match due to identical paternal chromosome from our father). Each color represents each of my 6 Great Grandparents DNA (Each of my Grandfathers fathers X's are not represented due to no male to male X transmission).

                          Two Family members happened to receive one of their mothers full single chromosome X which did not recombine with their mothers other single X. My paternal Uncle 2 and my Sister 3.

                          recombination rates are based on averages. In my family (not accounting for Father to daughter X inheritance, where father single X is passed on) the average recombination rate is approx. 1.83 (22 recombination points/12 people)

                          https://onedrive.live.com/redir?resi...hint=folder%2c
                          Last edited by prairielad; 9 September 2015, 12:42 AM.

                          Comment


                          • #14
                            I was circling back on this topic and found this gem [the link and screenshots...] posted by Prairielad. Absolutely awesome.

                            Many of us will never be able to accumulate this data on out own.

                            Thanks!!

                            I might suggest pulling this out and flagging it as a tutorial somehow. This and Matt Dexter's 4-Grandparents Phased chromosome browser screenshots.

                            Bob H.



                            Originally posted by prairielad View Post
                            Following attachments are of my Families X inheritance based on manually phasing our Raw Data files. Also shows the FTDNA chromosome browser shared sections between each of us (my sisters share is based on Gedmatch phased maternal data, as FTDNA show them as full match due to identical paternal chromosome from our father). Each color represents each of my 6 Great Grandparents DNA (Each of my Grandfathers fathers X's are not represented due to no male to male X transmission).

                            Two Family members happened to receive one of their mothers full single chromosome X which did not recombine with their mothers other single X. My paternal Uncle 2 and my Sister 3.

                            recombination rates are based on averages. In my family (not accounting for Father to daughter X inheritance, where father single X is passed on) the average recombination rate is approx. 1.83 (22 recombination points/12 people)

                            https://onedrive.live.com/redir?resi...hint=folder%2c

                            Comment


                            • #15
                              Originally posted by hansonrf View Post
                              I was circling back on this topic and found this gem [the link and screenshots...] posted by Prairielad. Absolutely awesome.

                              Many of us will never be able to accumulate this data on our own.

                              Thanks!!

                              I might suggest pulling this out and flagging it as a tutorial somehow. This and Matt Dexter's 4-Grandparents Phased chromosome browser screenshots.

                              Bob H.
                              The screen shots were actually provided by Earl Davis, in a thread both he and Matt were contributing to. Sorry for the error...

                              Bob H.

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