There has been a consistent pace of advancement in understanding gene regulation, microbiological evolutionary processes, and the systems of cellular machinery and regulation. There haven't been individual huge breakthroughs that are easy to point to and say "ahah! that's the lynchpin of everything, gimme a nobel!" but it's been a steady progression of improved knowledge. It'll be interesting to see if that trend continues and what that new understanding will translate into. In large part it's this stuff which is really fulfilling the promises of things like the human genome project.