送交者: xh 于 2005-3-17, 14:25:56:
回答: I am no expert on this 由 AI 于 2005-3-17, 13:36:41:
Nor is any text book. However, I think it is random in both levels.
At the DNA level, it is not predictable either, given that
1. genome size, it is hard to know before hand which base is going to be changed at any given time.
2. presence of different mechanisms that might cause mutation. Unless something is wrong, it is hard to tell which mechanism would work to cause a mutation at a given time.
After a mutation is recovered, it is possible that the cause of it can be traced. Beforehand, it can only be 'random'.
For DNA molecules, it does not matter which basepair is at a certain location. In that sense, there is no selection pressure at the DNA level. Hard to say what sequence has the least energy.
At fitness level, as I said before.