Regarding the modification aspect, there's already some (dubious) legislation applicable to (illegal) drugs which are similar, in that they differ only/primarily in non-functional ways: https://secure.wikimedia.org/wikipedia/en/wiki/Federal_Analo...

On the "found in nature" aspect, I believe some of the patented gene sequences are indeed derived directly from existing organisms, but are considered novel 'inventions' due to the labour and skill involved in identifying, isolating and applying them. Copyright doesn't really fit for that sort of use-case.