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Name: Vinsen
Status: student
Grade: 9-12
Location: Outside U.S.
Country: Indonesia
Date: N/A 


Question:
I was checking on the X-Chromosome Inactivation, which only happens on all females. When I read an article about this, a question suddenly sparks and I couldn't find any answer to it. The whole X-Chromosome Inactivation just doesn't mix well with X-Linked Diseases in females. If a female is having a recessive X-Linked Disease and suddenly the other X-Chromosome got inactivated, then it means that she will receive that disease right? If X-Chromosome Inactivation is true, then I Don't see why having less one X-Chromosome is lethal (Turner's Syndrome), is it because the only X-Chromosome got inactivated and letting the female to have no active X-Chromosomes?



Replies:
X inactivation occurs very early in development before differentiation happens. One X in each cell is inactivated at random. So if the woman is heterozygous, some cells contain the dominant gene and some the recessive gene. So the female is said to be a "mosaic". Since the x inactivation is random it is possible that all of the X's with the dominant gene could be inactivated which would effectively make the woman have the recessive trait. But that is highly improbable. It is possible to have more of the dominant X's inactivated and have a slight case. For example it is possible for a woman to have a mild case of hemophilia if she is a carrier. Turner Syndrome is not lethal. There are certain symptoms that are associated, but it isn't lethal. Also, new information suggests that not all of the genes on the X are inactive in normal X inactivation.

vanhoeck



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