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  #1  
Old 06-27-2013
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DNA X Chromosome Inactivation and X Linked Diseases

Hello everyone a quick question let's say a woman inherits an X linked recessive disease and the inactivation of the NORMAL x gene occurs making the x linked gene active does this woman express the gene or not? Im reading she doesn't express it because she has another X chromosome so hence the Barr body is not really inactive? So parts of the Barr body are active or not ? Or am i just missing something ?
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Old 06-27-2013
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I agree

good q i think she will develop the disease, remember the RB gene and disease in developing RB where the child inherits one defective gene and automutation imparts the other, setting the stage for the RB disease to show up. aint I right?
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Old 06-27-2013
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Yeah i understand RB tumor suppressor. You are right thats called loss of heterozygosity.

I just answered a question that stated the x linked recessive inheritance of g6pd def. in a female and marked that the x gene is active. I got it wrong and it says that the x linked phenotype is not usually expressed and answer wound up to be inheriting two X genes with g6pd mutation.

It seemed to be the obvious choice however i paid no attention to the fact that the mothers brother was affected and the father of the woman is affected meaning that the woman (mother) gave her the mutated X and the father only had a mutated x to give
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Old 07-01-2013
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OK everyone. I think i might have figured it out from reading First Aid.

You are more LIKELY to have a female express an x linked recessive disease due to two Mutated X chromosomes.

You are less likely to have random inactivation of a normal X chromosome (lyonization) resulting in expressing disease from mutated X chromosome.
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Old 07-02-2013
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Quote:
Originally Posted by haseebkat View Post
OK everyone. I think i might have figured it out from reading First Aid.

You are more LIKELY to have a female express an x linked recessive disease due to two Mutated X chromosomes.

You are less likely to have random inactivation of a normal X chromosome (lyonization) resulting in expressing disease from mutated X chromosome.
Also not all of the normal x chromosome will be inactivated... X inactivation is a random process and inactivation of abnormal x chromosome unlikely
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Old 07-02-2013
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Post just to add

Quote:
Originally Posted by haseebkat View Post
Hello everyone a quick question let's say a woman inherits an X linked recessive disease and the inactivation of the NORMAL x gene occurs making the x linked gene active does this woman express the gene or not? Im reading she doesn't express it because she has another X chromosome so hence the Barr body is not really inactive? So parts of the Barr body are active or not ? Or am i just missing something ?
just to add, it is still possible that a lady inheriting an x linked recessive gene can express the disease even without inheriting the a mutant gene from both the father and mother.

the phenomenon which I encountered on an nbme could be termed UNFAVORABLE X SKEWED INACTIVATION just as u cited in your post whereby more of the normal genes would be inactvated but the female might not show the same severity as the male would have.
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