Population genetics and molecular evoulution.

Recent studies of evolution and polymorphism at the molecular level (i.e, at the level of internal structure of the gene) have brought many puzzling as well as enlightening results. It appears that, in addition to natural selection, chance (in the form of random gene frequency drift) is playing a much larger part than previously considered. Futhermore, natural selection is likely to be based more directly on the secondary and the higher order structure of informational macromolecules rather than ecological conditions, usually in the form of negative selection. In this respect, there is growing evidence suggesting that very slightly deleterious mutations whose selective disadvantages are not excessively large as compared with the mutation rates are playing a significant role in variation and evoulution at the molecular level.