How does the original material differ from Sophocles' work?

As Sophocles' tragedy is based on the myth of Oedipus, how does the myth differ from the tragedy in that regard? Which parts of "Oedipus Rex" is derived from the myth and what has Sophcoles processed himself?

Which factor brought a turn to the plot and why?

What could be the modern equivalent to Greek Gods and fate as the element that determines our lives nowadays?