Science Buddies: "Ask an Expert"

I know this has been asked for before, but can anybody possibly find some information about the origin of the fourth leaf of white clover? I have seen sites that say genetic mutation, while others say trauma at birth. Nobody seems sure, at least nobody who'd be considered well based in biology.
I want to do a project about determining the effects of different soil content on the likelyhood of growing a four leaf clover, but I'd like to know what is known in the scientfic community about this possoble genetic mutation.

It really seems that this is still unknown - it might be simple recessive genetics, it might be a complex multi-gene thing, it might be a spontaneous mutation AND / OR it might have to do with environment (e.g. soil conditions).
for a bit more info see: http://en.wikipedia.org/wiki/Four-leaf_clover

You might also find some interesting information on the following site about trifolium repens - the "typical" clover plant from which 4-leaf clovers are occassionally found:
http://plants.usda.gov/java/profile?symbol=TRRE3

I looked a bit for scholarly articles on leaf number on this plant, but didn't find much. As legumes and Nitrogen fixers, they are important, and their growth in general is affected by phosphorous as well as other soil components, but I didn't find anything directly related to growth of the 4th leaf. Keep the board posted if you find something!