Re: can it be possible to alter one's biological sex with genetic enginneering?

	Anytime I'm asked a question like this, I get a little nervous just
saying, "no".�  Just a few years ago it would have been unthinkable to have
cloned sheep running around Scotland, but here we are.  Genetic engineering
is almost exclusively envisioned to treat illnesses (for this question,
we'll broaden it to "conditions") that involve one or a few genes gone
awry.   For instance, cystic fibrosis is known to be a defect of one amino
acid in one receptor and an astonishing number of genetic illnesses are
caused by single small mutations.  Introducing a single functioning gene
into a person stricken with one of these conditions is difficult, but
plausible with viruses and other vector based therapies.  To change the
genetic gender of a person, a scientist would have to introduce an entire
chromosome into a person.  The Y chromosome is the smallest in humans but
still codes for nearly eighty genes.  It is 58 megabases, a HUGE piece of
DNA to attempt to introduce into a cell.  Beyond that, the number of sex
chromosomes is important for genetic integrity.  For instance, if a woman
was to gain a Y chromosome in an attempt to change her genetic gender, she
would be XXY (the new Y chromosome plus the two X chromosomes she was born
with).  People who are XXY often are stricken with a disease called
Klinefelter's disease, which can predispose them to a number of illnesses.
 Thus, an effective therapy would not only need to introduce the new sex
chromosome, but somehow remove the unnecessary chromosome.  I will say
that, if it were possible to remove an entire chromosome from a cell and
reintroduce another, single celled embryos would probably be the only point
during development when gender could be reassigned.  Even under the best of
circumstances during genetic engineering of other organisms (from bacteria
to mice), only a subset of cells are ever truly altered.   Thus, if
traditional genetic engineering approaches used on lab animals were
attempted in humans, some cells would be male and some cells would be
female.
	Finally, it is important to understand that while genetics play a huge
role in gender assignment, the effect of hormones and other cellular
signals during development cannot be ignored.  During pregnancy, a fetus is
exposed to a great deal of hormones that imprint their effects on the
developing child.  Many secondary sex traits are irrevocably formed during
this time, and there is mounting evidence that this is when the brain is
assigned a gender - male or female.  Simply changing the chromosomal
complement of a person would not change these effects.  
	So, I am going to go out on a limb here and say that, at least for now,
gender reassignment on a genetic level is not possible.
Billy.


I have included some Wikipedia articles here for your reference  - caveat,
though, that Wikipedia should never be used as a reference in any kind of
formal paper.

Klinefelter's Syndrome. http://en.wikipedia.org/wiki/Klinefelter%27s_syndrome

Transformation. http://en.wikipedia.org/wiki/Transformation_%28genetics%29

Y chromosome. http://en.wikipedia.org/wiki/Y_chromosome

Sex determination system. http://en.wikipedia.org/wiki/Sex-determining