Again Ryu_Kaze, I have to stand a little bit more firmly on the difference between Jenova's biological material and Sephiroth's. Jenova isn't "basically Sephiroth." Sephiroth was a combination of Hojo's DNA, (assuming they even have DNA in the FFVII Universe), Lucretia's DNA, and Jenova cells. I don't see anything inherent in Jenova's biological material that could make her turn into Sephiroth.
However there is the mimic ability, which does in fact creates physical manifestations of things (as opposed to mental projections/illusions). This is evidenced by the sword of the "ghost" Sephiroth we chase throughout FFVII(who is Jenova's body manifested as Sephiroth) being stabbed into a certain few characters.
However, the rest of this topic is very informative, and I don't see any other obscurities. Thanks again.
Sephiroth got Jenova cells while he was a fetus. Jenova cells probably make up most, if not all of his being. How do you figure? Do you think that since he was a fetus the Jenova cells just jumped right into his DNA, giving the command "differentiate like this?"
Sephiroth was a _human_ enhanced by Jenova, not comprised of Jenova.