What will be the biggest benefit for human beings from mapping the human genome?

Update: Most of the best answers talked about medical benefits from decoding the genome though even the most knowledgeable of you were rather vague about the benefits to come. That's understandable; at this point nobody knows where our research efforts will lead. Genetics has diagnostic potential but many scientists... show more Most of the best answers talked about medical benefits from decoding the genome though even the most knowledgeable of you were rather vague about the benefits to come. That's understandable; at this point nobody knows where our research efforts will lead. Genetics has diagnostic potential but many scientists believe that in a few years proteins will prove to be more useful. The whole field is in flux.
A number of you mentioned immortality. There has certainly been a lot of speculation about that, but many lines of research lead me to feel quite certain that immortality is not in our future. It's fun to think about, but don't hold your breath.
I choose the answer from ZERO COOL because it focused on realistic outcomes, including rational drug design, early detection of genetic predisposition to disease, and custom drugs. And the author seems to have a firm grasp of exactly how we move from symptomatic treatment to addressing disorders at a fundamental level.
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