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Thread: Grandfather's X chromossome Inheritance

  1. #1
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    Grandfather's X chromossome Inheritance

    So, this image is my X and both my grandmother's X compared we seem to share only the tip of our Xs, by proportions it seems like >10% <20% of it, so I basically have my maternal grandfather X chromo. This is so small in fact that a random woman with no autossomal matches with my grandma shares more X with her than me, her own grandson. is this normal? or under a "normality"?

    I'm only concerned to the fact that my grandfather is going bald, but I looked up the genes I don't think I have the balding gene there, would I have escaped with the tiny piece from my grandma? luck?

    Last edited by Kaipiro; 11-08-2018 at 01:31 PM.
    Haplogroups:

    Paternal
    E-V13 > Z5018 > Z16242
    (-Z2162, -BY5253)
    Southern Brazil > São Paulo > Portugal


    Maternal:
    D > D4 > D1
    Northeastern Brazil > Indigenous American> Bering Strait/Asia

  2. #2
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    Pittsburgh, PA, USA
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    United Kingdom Germany Bayern Catalonia France Ireland Switzerland
    Quote Originally Posted by Kaipiro View Post
    So, this image is my X and both my grandmother's X compared we seem to share only the tip of our Xs, by proportions it seems like >10% <20% of it, so I basically have my maternal grandfather X chromo. This is so small in fact that a random woman with no autossomal matches with my grandma shares more X with her than me, her own grandson. is this normal? or under a "normality"?

    I'm only concerned to the fact that my grandfather is going bald, but I looked up the genes I don't think I have the balding gene there, would I have escaped with the tiny piece from my grandma? luck?

    Since you recognize that the DNA on your X chromosome that you don't share with your maternal grandmother must have come from your maternal grandfather, I don't understand why you seem amazed that "a random woman with no autossomal matches with my grandma shares more X with her than me, her own grandson". You simply share this DNA with your maternal grandfather and his mother instead. Why would your grandmother share autosomal DNA with either her husband or her mother-in-law? (Yes, they could be related -- but I presume you'd know it if they were.)

    What you're seeing is nothing unusual. In fact, it's possible for a male to share no X-chromosome DNA with his maternal grandmother.

    The graphic below shows how my oldest brother Bernie, our sister Kim, and I match on the X chromosome.

    Bernie - Kim and Gary - X.JPG
    Bernie versis Kim & Gary on X chromosome.jpg

    As you can see, Kim and Bernie match across the entire X chromosome except for the very tips. This actually doesn't mean they don't match at the tips, but simply that FTDNA doesn't believe there are enough tested SNPs here to be able to tell. (23andMe does show these siblings matching at the tips of the X chromosome.)

    Based on the matching of my siblings to various cousins, it's possible to say that this X came entirely from our mother's father, and therefore from our mother's paternal grandmother.

    That means that my brother Bernie doesn't share anything at all on the X chromosome with our maternal grandmother. Nor does our sister Kim. And I share less with my maternal grandmother than you do with yours -- only about 20 cM.

    As you can see from the graphic, there's only a small region in which I don't match these two siblings. As I said, the regions where we do match came from our mother's father, so the region where we don't came from our mother's mother in my case.

    I know it's from my maternal grandmother because I match some maternal half 2nd cousins across this region. I also know it came from my grandmother's mother, because my matches here are all descendants of my grandmother's maternal half sisters.
    Last edited by geebee; 11-08-2018 at 05:47 PM. Reason: To reflect re-reading of OP
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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  4. #3
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    Quote Originally Posted by geebee View Post
    Since you recognize that the DNA on your X chromosome that you don't share with your maternal grandmother must have come from your maternal grandfather, I don't understand why you seem amazed that "a random woman with no autossomal matches with my grandma shares more X with her than me, her own grandson". You simply share this DNA with your maternal grandfather and his mother instead. Why would your grandmother share autosomal DNA with either her husband or her mother-in-law? (Yes, they could be related -- but I presume you'd know it if they were.)

    What you're seeing is nothing unusual. In fact, it's possible for a male to share no X-chromosome DNA with his maternal grandmother.

    The graphic below shows how my oldest brother Bernie, our sister Kim, and I match on the X chromosome.

    Bernie - Kim and Gary - X.JPG
    Bernie versis Kim & Gary on X chromosome.jpg

    As you can see, Kim and Bernie match across the entire X chromosome except for the very tips. This actually doesn't mean they don't match at the tips, but simply that FTDNA doesn't believe there are enough tested SNPs here to be able to tell. (23andMe does show these siblings matching at the tips of the X chromosome.)

    Based on the matching of my siblings to various cousins, it's possible to say that this X came entirely from our mother's father, and therefore from our mother's paternal grandmother.

    That means that my brother Bernie doesn't share anything at all on the X chromosome with our maternal grandmother. Nor does our sister Kim. And I share less with my maternal grandmother than you do with yours -- only about 20 cM.

    As you can see from the graphic, there's only a small region in which I don't match these two siblings. As I said, the regions where we do match came from our mother's father, so the region where we don't came from our mother's mother in my case.

    I know it's from my maternal grandmother because I match some maternal half 2nd cousins across this region. I also know it came from my grandmother's mother, because my matches here are all descendants of my grandmother's maternal half sisters.
    interesting case, thanks for sharing. I am amazed cause everyone else seems to have a good chunk of their X from their maternal grandmother (friends that tested). It is also to prove that those X chrome inheritance charts are flawed and are not "precise math", they are simply illustrative.
    Haplogroups:

    Paternal
    E-V13 > Z5018 > Z16242
    (-Z2162, -BY5253)
    Southern Brazil > São Paulo > Portugal


    Maternal:
    D > D4 > D1
    Northeastern Brazil > Indigenous American> Bering Strait/Asia

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