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Thread: Genetics: X chromosome inactivation

  1. #1 Genetics: X chromosome inactivation 
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    Hello,
    I was hoping someone can help clarify these questions.

    1. What is X chromosome inactivation (lyonization)?
    a) does it occur in every cell?
    b) (for females) can different parents X chromosomes be activated in different
    cells?
    2. Do males have X chromosome inactivation as well?

    Thanks for your time, effort and thought into this


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  3. #2  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    1.
    a) every cell except the eggs.
    b) It happens at random early in embryonic development, so usually you'll find patches of cells with the same X chromosome inactivated. The classic example of this is the calico cat, the unique coat colour distribution of each calico is caused by the random inactivation of X chromosomes in embryonic development.

    2. Only in XXY men, so not in normal men.


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  4. #3  
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    Thanks for sharing.
    The calico cat can have orange and black patches.
    Does this mean different inactivation of genes are occuring?
    Is it possible for a female child to have different chromosomes activated in cells?
    So in one cell her mother's X chromosome is activated,
    and in another her father's X chromosome?
    Does the Y chromosome ever "lyonize" as well?

    Furthermore,
    What is the purpose for this inactivation? Why does it happen?

    I wish my local college offered a genetics class lol
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  5. #4  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Quote Originally Posted by lilyspetal
    Thanks for sharing.
    The calico cat can have orange and black patches.
    Does this mean different inactivation of genes are occuring?
    Is it possible for a female child to have different chromosomes activated in cells?
    So in one cell her mother's X chromosome is activated,
    and in another her father's X chromosome?
    Does the Y chromosome ever "lyonize" as well?

    Furthermore,
    What is the purpose for this inactivation? Why does it happen?

    I wish my local college offered a genetics class lol
    First the calico cat. The genes determining coat colour in calico cats are carried on the X chromosome, there are a few different genes at play but basically to understand it just picture it as one X says Black, one says Orange, so depending on which is being expressed you get that colour on the patch.

    Yes, it happens during embryonic development so when there are like 50 cells (I don't know the actual point of the top of my head) those 50 cells will then randomly inactivate one of the X chromosomes. Now all cells that derive from those 50 will have the same X chromosome inactivated.

    The Y chromosome does not get inactivated, men only have one.

    Well you only need one X chromosome to encode the genes you need, so a second is superfluous. (Males operate with only one X chromosome so it makes sense that women do too.)
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