From what I understand of Superman, his powers come from a combination of a dense molecular structure, energy absorbed from a yellow sun, and some souped up organs (like his eyes and xray vision and all that, basically a better eye than a human's).
Now, the dense molecular structure and other physiological factors would probably be passed on through genes. Remember, in Superman 2, he was made MORTAL, not HUMAN. So, he still had the genes and the potential to have his powers. His powers were taken away because the red sun rays cancelled out the effect the yellow sun had on him temporarily or something like that.
I'm not 100% sure, but I know that Superman without exposure to yellow sun is basically a lot like a human being. He absorbs energy from a yellow sun and his body stores it and uses it to give him some of his powers.
If you seriously want to know about this stuff, there have been some books written about the science and/or physics of Superman.
Cliffs: Superman is like a rechargable battery. Yellow sun is the battery charger. Superman without yellow sun still has the potential to have powers, but lacks the juice.