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  • Newbe Questions from a man

    I have been filly tested on my Y chromosome and beginning to wonder about my X chromosome which I know comes from my mother.

    My burning question is that I have 3 daughters, 2 by my first wife, and one by my second wife, so when a woman is tested how do the scientists know which X chromosome came from the father and which came from the mother??

    The answer could be as simple as a woman has a strand of dna from each parent and the scientists know how to tell the mother's strand from the father's strand based on the position at top or bottom of the X chromosome. Like we always see the X chromosome picture as an X shape. Father's strand is one that starts on left, mother's on right, or visa versa.

    I do not know why I wonder this, but I do.

    Thank You
    David Christopher

  • #2
    You posted about the X chromosome, but in the mtDNA section. As you know, these are different.

    It is a limitation of current technology that everyone gets back a raw data file with the positions for both sides (maternal and paternal) of the chromosome, without any way to tell them apart, including for the X in women. I read in the Ancestry white paper that it is theoretically possible to make this separation, but prohibitively expensive.

    Thus, people use all sorts of workarounds to determine if a match is real. In principle, a match between two people (such as two women on the X chromosome) can zigzag back and forth between the parental sides to create what looks like a half-identical region that is not actually real. The higher the cMs and SNPs, the less likely such a false match has occurred. If the two parents have very different ethnicities, false matches are less likely. If two parents have the same background, then false matches are more likely.

    People also phase their data with a parent's data. That likely means that you have a much higher probability of a true match with a phased kit, but if you do actually have your parents' data, you'll miss out on a lot of matches that they have (but which could potentially be false).

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    • #3
      No I did not know there is a difference

      Between X chromosome and mtDNA. Looks like I am going back to study what is in a sperm and what is in an egg. I thought an egg has only an X and a sperm can have an X or a Y, and the other 22 chromosomes in egg and sperm were half of a chromosome that joined with their counterpart to make an entire chromosome that has 2 X's or one X and one Y.

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      • #4
        David, try some of these links, which may help you differentiate mtDNA and the X chromosome. It does get confusing!
        From the Learn Genetics Genetic Science Learning Center, Chromosomes and Inheritance videos:
        X Chromosome DNA
        Mitochondrial DNA

        From Kelly Wheaton's Beginner's Guide to Genetic Genealogy, An Overview of the Types of DNA Used by Genetic Genealogists
        Use the chart she references at the top of that page; the link for it is lower on the page, after the black/grey text.

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        • #5
          OHHH Thank you

          So the X is just like Autosomal in how it is reconstructed. The mitochondrial DNA is the equivalent of how I think of the Y chromosome.

          So if I get the mt test it is going to analyze the mitochondrial dna which comes from my mother which came from her mom and so on.

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          • #6
            chrstdvd: Good Catch! The X is actually Chromosome 23. It just has a different inheritance path, and a different cMs threshold for matches than autosomal chromosomes 1-22. And the X has a different threshold according to gender.

            And, yes, the Y is father-to-father-to-father upstream back in time.
            MtDna is mother-to-mother-to-mother upstream back in time.
            Last edited by Biblioteque; 12th July 2016, 05:55 PM.

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            • #7
              Originally posted by chrstdvd View Post
              So the X is just like Autosomal in how it is reconstructed. The mitochondrial DNA is the equivalent of how I think of the Y chromosome.

              So if I get the mt test it is going to analyze the mitochondrial dna which comes from my mother which came from her mom and so on.
              One difference you should be aware of before shelling out money - the mitochondrial DNA gives way less in the way of genealogical information - a perfect match may mean a common ancestor many, many generations back. So, if your goal is most bang for the buck in the way of genealogical information, probably do not bother with testing it unless / until you have an hypothesis you are trying to test. [Most bang for buck is probably FamilyFinder - if you have not done that, then strongly recommend order it as an upgrade.]

              (Despite what I know about MtDNA, I went ahead and did it - for myself and for two relatives who go back along their maternal line to one of my ancestors - and no, it has not provided me with any insights at all. But - if I ever get a close - or possibly even a 2nd-4th- FamilyFinder match who also is an exact match to one of those (and not an already known relative) - then I will start getting excited.)
              Last edited by loobster; 12th July 2016, 07:39 PM.

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              • #8
                also note that we have two of each chromosome, except in the respect to X in males who have 1 X from mother and a Y from father.

                These are not half of chromosomes from each parent that join together in child. Each of their two pairs randomly recombined to form a complete single chromosomes to child.

                We each have 23 single maternal chromosomes and 23 single maternal chromosomes, 46 single chromosomes in total.
                Each single maternal and paternal chromosomes of each pair contain the same SNPs/position tested, they just can have different values for each SNP(A,C,G,and T)

                The pictures of Chromosomes you see in shape of X, is just that single chromosomes in the process of replicating/dividing. Each side is identical
                Attached Files
                Last edited by prairielad; 12th July 2016, 11:15 PM.

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                • #9
                  Loobster is on track. If, for example, you are trying to rule out Native American ancestry on you matralinial line, they have their own Haplogroups, so this could be easily done.
                  Worked for me.
                  Last edited by Biblioteque; 13th July 2016, 09:22 AM.

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                  • #10
                    Meant to say rule NA ancestry in OR out on the matralineal line.

                    So why doesn't FTDNA use this in their advertising and open up a new target market. It would sell more mtDNA testing.......
                    Last edited by Biblioteque; 13th July 2016, 09:42 AM.

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                    • #11
                      mtDNA & Haplogroups

                      Not a reply but I was intending to ask this question and it seemed to fit here {rather than starting another thread!}

                      If I were to test my brother {he has done a Y test}for mtDNA full will his Haplogroup be the same as mine {same mother and father}?

                      I ask because I have one of the more unusual ones.

                      Comment


                      • #12
                        same mother, same haplotype.

                        It is a terminal situation for your brother, however. While he has the same mtDNA haplotype, he will not pass it down to his kids, as they will receive their mother's mtDNA.

                        The Y DNA will not affect that. Other than you can use the same kit to do a mtDNA test.

                        If your mother has any sisters, they will also have the same haplotype, as well as all of their kids, male or female.

                        All of you descend from your maternal grandmother who also had the same haplotype, as did her mother and her mother etc.

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                        • #13
                          Originally posted by betadams View Post
                          Not a reply but I was intending to ask this question and it seemed to fit here {rather than starting another thread!}

                          If I were to test my brother {he has done a Y test}for mtDNA full will his Haplogroup be the same as mine {same mother and father}?

                          I ask because I have one of the more unusual ones.
                          As user mabrams wrote above, both of you got your mtDNA from your (common) mother.

                          So you are guaranteed the same haplogroup. However, there could be differences in your mtDNA results, as mutations happen - we just do not know when.

                          The same haplogroup, but not necessarily identical mtDNA.

                          Mr W

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                          • #14
                            mabrams and Mr W

                            Thank you for your replies.

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