Inactivation of X Chromosomes
Location: Outside U.S.
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?
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.
Click here to return to the Molecular Biology Archives
Update: June 2012