Well, increasing the beta-carotene also makes the rice kinda orange-y and obviously it costs some energy from the rest of the plant. Though that's maybe not qui

Well, increasing the beta-carotene also makes the rice kinda orange-y and obviously it costs some energy from the rest of the plant. Though that's maybe not quite what you mean. Lots of genes only seem to do one thing. HERC2 seems to only affect eye color. If you're asking if it's possible that maybe we don't have a 100% perfect understanding of genetics, then of course it's possible. It's always possible there's something we don't know. Science does not deal in perfect certainties. Would I be correct is following your logic to the implication that there's a significant possibility for effects we didn't anticipate and don't understand in genetic engineering? Of course that's possible. That's why GMOs are tested. Is it possible that there's some obscure, subtle side-effect we won't notice for a long time to come? Yes. Is it likely? As near as we can tell, no. Can this doubt ever be fully assuaged by science? Not reasonably on anything more complex than the simplest of yeasts. Is this a special threat, uniquely applicable only to GMOs? No. The same potential is present - even greater, due to number of mutations - in selective breeding.