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  • The male X chromosome

    We get an X chromosome full of SNPs from our mother at birth.It is nearly three time bigger than the Y so the X chromosome has been around three time longer than the Y.There is little or no recombination in this X so why cant it be used to trace the female line. Does that make sense?

  • #2
    Originally posted by 1798 View Post
    We get an X chromosome full of SNPs from our mother at birth.It is nearly three time bigger than the Y so the X chromosome has been around three time longer than the Y.There is little or no recombination in this X so why cant it be used to trace the female line. Does that make sense?
    We need to clarify the recombination here. While the X travels through the male, there is no recombination except at the tips. He matches his mother, but not just a match with one of her two Xs. She mixes (recombines) her two Xs before passing one to her son. So it does not trace just the female line. Segments of this male's X could have come from both the mother's mother and the mother's father.

    When the X travels through a female, it behaves like an autosome. When the X travels through the male, it behaves more like the Y by remaining intact.

    The X can trace a female line, but segments often travel through males as long as there are no two males in a row, meaning there cannot be transmission from a father to a son.

    I don't think the size of the chromosome has anything to do with the age of the X compared to the Y.

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    • #3
      Originally posted by Kathy Johnston View Post
      We need to clarify the recombination here. While the X travels through the male, there is no recombination except at the tips. He matches his mother, but not just a match with one of her two Xs. She mixes (recombines) her two Xs before passing one to her son. So it does not trace just the female line. Segments of this male's X could have come from both the mother's mother and the mother's father.

      When the X travels through a female, it behaves like an autosome. When the X travels through the male, it behaves more like the Y by remaining intact.

      The X can trace a female line, but segments often travel through males as long as there are no two males in a row, meaning there cannot be transmission from a father to a son.

      I don't think the size of the chromosome has anything to do with the age of the X compared to the Y.
      The X chromosome looks like the dominant one.Why has the X chromosome three times the amount of SNPs compared to the Y?

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      • #4
        Originally posted by 1798 View Post
        The X chromosome looks like the dominant one.Why has the X chromosome three times the amount of SNPs compared to the Y?
        The X has more SNPs than they Y because the X chromosome is longer in length. Chromosome 1 is even longer, and it has more SNPs, but doesn't make it dominate over the X.

        Two Xs in the female and one X in the male does not make the X dominate because gender is not determined by combination of all 4 (or a 3:1 ratio). Gender is determined by which 23rd chromosome is inherited from just the father which means out of X or Y, the child will receive just one (a 1:1 ratio, or 50% chance of either an X or a Y from the father).


        Matt.

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        • #5
          Originally posted by mkdexter View Post
          The X has more SNPs than they Y because the X chromosome is longer in length. Chromosome 1 is even longer, and it has more SNPs, but doesn't make it dominate over the X.

          Two Xs in the female and one X in the male does not make the X dominate because gender is not determined by combination of all 4 (or a 3:1 ratio). Gender is determined by which 23rd chromosome is inherited from just the father which means out of X or Y, the child will receive just one (a 1:1 ratio, or 50% chance of either an X or a Y from the father).


          Matt.
          This is what I mean.The x chromosome has 155 million base pairs, longer than chromosome 8 but shorter than 7. There are more than 2 million SNPs discovered so far.

          The y chromosome has only 60 million base pairs, about the same as chr 19 and 20. It has fewer than 200K SNPs discovered.

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          • #6
            Originally posted by 1798 View Post
            This is what I mean.The x chromosome has 155 million base pairs, longer than chromosome 8 but shorter than 7. There are more than 2 million SNPs discovered so far.

            The y chromosome has only 60 million base pairs, about the same as chr 19 and 20. It has fewer than 200K SNPs discovered.
            That doesn't make it less dominate than an X, just because it is smaller. I don't see the point.

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            • #7
              There really is no male X chromosome.Both X chromosomes are female.We men get an X from our mothers and pass it on to our daughters.The other X is passed on from female to female.
              The Y looks tiny compared to the X and both Xs are similar in size.All the other chromosomes from 1-22 are similar in size.
              SNPs happen over thousands of years so the X must be older than the Y.

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              • #8
                Originally posted by 1798 View Post
                There really is no male X chromosome.Both X chromosomes are female.
                Just because the X chromosome doesn't recombine in males doesn't mean there is no male X chromosome.

                Originally posted by 1798 View Post
                We men get an X from our mothers and pass it on to our daughters.The other X is passed on from female to female.
                The other X isn't strictly passed from female to female. The X chromosome contributed to a daughter by the mother is a combination of that mother's own X chromosomes received from her mother and father.

                http://www.thegeneticgenealogist.com.../NewChart5.jpg

                Originally posted by 1798 View Post
                The Y looks tiny compared to the X and both Xs are similar in size.All the other chromosomes from 1-22 are similar in size.
                SNPs happen over thousands of years so the X must be older than the Y.
                The age of chromosomes isn't based on size. It's currently believed that the X and Y chromosomes diverged in mammals sometime between 160 and 300 million years ago, and they've existed concurrently since this time.

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                • #9
                  Originally posted by 1798 View Post
                  There really is no male X chromosome.Both X chromosomes are female.We men get an X from our mothers and pass it on to our daughters.The other X is passed on from female to female.
                  The Y looks tiny compared to the X and both Xs are similar in size.All the other chromosomes from 1-22 are similar in size.
                  SNPs happen over thousands of years so the X must be older than the Y.
                  I'd be happy to help you understand this better but I do not know if you are actually asking for help. Some of the statements you have made about the X and Y do not really correlate to using the X chromosome to find related connections in the Family Finder test database.

                  A large segment match (such as a block over 7cM) on the X chromosome between two individuals will indicate a relation, especially if one or both of them is a male. Since the X is not passed down from father to son, this creates a more unique inheritance pattern than that of the autosomal DNA and thus can be used in a more specific manner when two people have a Family Finder X chromosome match. That is why the X is unique, not because of its size or age or any other feature as far as DNA test matching is concerned.

                  Now, if you were asking, it works like this: A male has one X chromosome that he inherited from his mother. That one X chromosome is his, but did come from his mother, meaning it is a male X chromosome from his maternal side. In reality, it is a copy of the first X chromosome he had which came from the egg supplied by the mother. I suppose we could disagree on whether it is a female or male X in this case yet in the case of his daughter, we would have to then say she has a male X and a female X. That is not really the way to describe any of it. This is how I would describe it.

                  A male will have 23 pairs of chromosomes. In his 23rd pair will be a maternal X chromosome and a paternal Y chromosome, both making up the DNA of a male in this case. So while he has only one X chromosome, it is his, thus a male X chromosome from the maternal side and is paired with a Y chromosome from his paternal side.

                  A female also has 23 pairs of chromosomes. In her 23rd pair will be a maternal X chromosome and a paternal X chromosome, both making up the DNA of a female in this case. So while she has two X chromosomes, they are both female X chromosomes, one from the paternal side, one from the maternal side.

                  So there is a difference between where the chromosomes are inherited from but not all X chromosomes are female. In the male, they are male inherited from his maternal side, in a female, they are female inherited one from the maternal side, and one from the paternal side.

                  Hope that helps.

                  Matt.
                  Last edited by mkdexter; 10 April 2014, 01:40 AM.

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                  • #10
                    Originally posted by mkdexter View Post
                    I'd be happy to help you understand this better but I do not know if you are actually asking for help. Some of the statements you have made about the X and Y do not really correlate to using the X chromosome to find related connections in the Family Finder test database.

                    A large segment match (such as a block over 7cM) on the X chromosome between two individuals will indicate a relation, especially if one or both of them is a male. Since the X is not passed down from father to son, this creates a more unique inheritance pattern than that of the autosomal DNA and thus can be used in a more specific manner when two people have a Family Finder X chromosome match. That is why the X is unique, not because of its size or age or any other feature as far as DNA test matching is concerned.

                    Now, if you were asking, it works like this: A male has one X chromosome that he inherited from his mother. That one X chromosome is his, but did come from his mother, meaning it is a male X chromosome from his maternal side. In reality, it is a copy of the first X chromosome he had which came from the egg supplied by the mother. I suppose we could disagree on whether it is a female or male X in this case yet in the case of his daughter, we would have to then say she has a male X and a female X. That is not really the way to describe any of it. This is how I would describe it.

                    A male will have 23 pairs of chromosomes. In his 23rd pair will be a maternal X chromosome and a paternal Y chromosome, both making up the DNA of a male in this case. So while he has only one X chromosome, it is his, thus a male X chromosome from the maternal side and is paired with a Y chromosome from his paternal side.

                    A female also has 23 pairs of chromosomes. In her 23rd pair will be a maternal X chromosome and a paternal X chromosome, both making up the DNA of a female in this case. So while she has two X chromosomes, they are both female X chromosomes, one from the paternal side, one from the maternal side.

                    So there is a difference between where the chromosomes are inherited from but not all X chromosomes are female. In the male, they are male inherited from his maternal side, in a female, they are female inherited one from the maternal side, and one from the paternal side.

                    Hope that helps.

                    Matt.
                    Thanks Matt.
                    A woman is female because she has two X chromosomes so both are female.One of the Xs would be very hard to trace because it recombines but the other doesn't. So the females can trace one of their maternal lines through the so called "male" X.
                    I have 14 X matches and I have examined the SNPs that we match and none of them have combined alleles like the 1-22 chromosomes.
                    My question is why doesn't someone put together an X tree for this female line? Does that make sense?

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                    • #11
                      Doesn´t make much sense to me, but then maybe I have misunderstood all of the literature I have read explaining the X-chromosome inheritance patterns

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                      • #12
                        Originally posted by 1798 View Post
                        Thanks Matt.
                        A woman is female because she has two X chromosomes so both are female.One of the Xs would be very hard to trace because it recombines but the other doesn't. So the females can trace one of their maternal lines through the so called "male" X.
                        I have 14 X matches and I have examined the SNPs that we match and none of them have combined alleles like the 1-22 chromosomes.
                        My question is why doesn't someone put together an X tree for this female line? Does that make sense?
                        You need to be able to follow the whole chromosome back for multiple generations. This is possible for the Y and mtDNA, because they don't break up.

                        The X a woman receives from her father is indeed exactly like his X. It didn't break up for one generation. But he got his X from his mother, whose two X chromosomes underwent the recombination process to make his one X chromosome. Brothers will (almost always) have different X chromosomes. See this animation

                        http://www.smgf.org/education/animat...hromosome.jspx

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                        • #13
                          Thanks Ann.
                          I have 17,509 X SNPs from Family Finder.
                          AA 24%
                          GG 26%
                          TT 24%
                          CC 26%
                          From what I have read these are only a small percentage of the whole X chromosome but you say that they were recombined before they were passed on to me.

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                          • #14
                            Originally posted by 1798 View Post
                            Thanks Matt.
                            A woman is female because she has two X chromosomes so both are female.One of the Xs would be very hard to trace because it recombines but the other doesn't. So the females can trace one of their maternal lines through the so called "male" X.
                            I have 14 X matches and I have examined the SNPs that we match and none of them have combined alleles like the 1-22 chromosomes.
                            My question is why doesn't someone put together an X tree for this female line? Does that make sense?
                            I gather that you are a male so when you say combined alleles do you mean you are getting all homozygous (e.g. AA) instead of heterozygous (e.g. AG) results? That could also be causing some confusion. If all your alleles are the same such as AA, CC, GG, TT, TT etc. you need to subtract out one from each position for your one X chromosome. FTDNA lists these in duplicate. The software doesn't know you are a male even though it would be obvious to us by looking at the results. The chip sees only an A for position #1 so lists it as AA. For example, if no Gs fall into position #1 then you get AA. A female with two As will get AA but if she had one A and one G, the result would come out AG. Quite often women do have a long run of homozygous results on her two Xs but not the entire length. Males will show two alleles at each position in the FTDNA software but that is not real because he only has one X. Get rid of one of your alleles at each position.

                            This may not be what you are referring to but I doubt that you have examined the raw data of all 14 of your matches. They would have to send that to you. I bet you have just examined your own results.

                            Kathy
                            Last edited by Kathy Johnston; 10 April 2014, 01:03 PM.

                            Comment


                            • #15
                              Originally posted by Kathy Johnston View Post
                              I gather that you are a male so when you say combined alleles do you mean you are getting all homozygous (e.g. AA) instead of heterozygous (e.g. AG) results? That could also be causing some confusion. If all your alleles are the same such as AA, CC, GG, TT, TT etc. you need to subtract out one from each position for your one X chromosome. FTDNA lists these in duplicate. The software doesn't know you are a male even though it would be obvious to us by looking at the results. The chip sees only an A for position #1 so lists it as AA. For example, if no Gs fall into position #1 then you get AA. A female with two As will get AA but if she had one A and one G, the result would come out AG. Quite often women do have a long run of homozygous results on her two Xs but not the entire length. Males will show two alleles at each position in the FTDNA software but that is not real because he only has one X. Get rid of one of your alleles at each position.

                              This may not be what you are referring to but I doubt that you have examined the raw data of all 14 of your matches. They would have to send that to you. I bet you have just examined your own results.

                              Kathy
                              I have examined the 500 snps of each of the 14 matches.

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