I was wondering if when you wrote "Ender's Game" in the novel form, if you had any backstory with Bean that might have included Anton's Key? Also, where did you get the idea for Bean's genetic difference?
There was no plan for Bean beyond the events in Ender's Game. Anton's Key was not thought of until I was in the midst of writing Ender's Shadow. I didn't get the idea for Bean's genetic difference from anywhere - I simply asked myself, how might Bean be different from Ender, and yet just as capable? Since he's living on the street as an orphan (I thought of that first), how would he overcome the huge advantage Ender would have by having been raised with good, attentive parents and having every advantage as a growing child? And this genetic difference was the best idea that came to mind - the one that made me say, Yes! That's it!