>>26
Many species, such as flies, have much larger numbers of "sex" chromosomes than humans and manifest gender on a completely different system than the traditional punit square. Humans, on the other hand, only posses more than 2 sex chromosomes as a mutation.
Individuals with XXY chromosomes inevitably suffer the normal genetic problems associated with having extra chromosomes. Many physically and mentally retarded individuals have this problem with other chromosome pairs (although i am unsure if individuals with extra "sex" chromosomes have developmental problems similar to those of most retarded persons.)
Certain species of frogs (like the ones referred to in the Jurassic Park movies) have the capacity to "adjust" their gender from female to male by undergoing a hibernation process, and emerge a member of the opposite sex. However, they are capable of such mutations only because of their additional sex chromosomes.
Dual gender "chimeras" are inevitably infertile, and most of those who manifest the sexual characteristics of both genders from birth are actually possessed of only one gender and simply have birth defects.
"Gender adjustment procedures" and other forms of plastic surgery are, despite popular belief, incapable of actually altering an individual's gender, because no amount of plastic surgery can change DNA. Also, such an individual's reproductive organs cannot be "retrofitted" to perform the function of those of the opposite gender. It might indeed be possible to transplant the organs of another, but the chance of rejection is, naturally, very high.
Although their are indeed methods of inserting genes into an specimen, it is questionable whether or not changing entire chromosomes will be feasible even in the distant future. Additionally, any attempts to insert genes into a living higher-order organism, such as a human being, would either be unsuccessful or deadly to the subject.