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Sex linked diseases and lyonization in females

  1. Feb 6, 2017 #1
    Suppose, there's a disease "D", which is an X-linked, dominant disease.
    Now, there's a female who possesses the allele for this disease in one of her two X chromosomes. (XDX)

    It's easy to say that since the allele for the disease is dominant, she'll suffer from it.

    Now, it's a well known fact that in females, one of the X chromosomes gets inactivated ( Barr Body formation or lyonization).

    My question is, how can we be sure that she will suffer from the disease? We can never be 100% sure!

    What if the X chromosome, which has the allele for the disease, is the one that gets inactivated ? That allele will never be expressed and she'll never suffer from the disease.
  2. jcsd
  3. Feb 6, 2017 #2


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    X-inactivation is a random process, so approximately 50% of the cells in a woman's body will have the paternal X inactivated and 50% will have the maternal X inactivated. Unless the number of cells causing the dominant phenotype is very small, there will likely be some population of cells expressing the dominant allele to cause the disorder. Wikipedia lists a few examples of dominant X-linked disorders (https://en.wikipedia.org/wiki/X-linked_dominant_inheritance).
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