On April 14, 2003, scientists announced to the world that they had finished sequencing the human genome--logging the three billion pairs of DNA nucleotides that describe how to make a human being. But finding all the working genes amid the junk in the sequence remains a further challenge, as does gaining a better understanding of how and when genes are activated and how their instructions affect the behavior of the protein molecules they describe. So it is no wonder that Human Genome Project leader Francis S. Collins has called the group's accomplishment only "the end of the beginning."

Collins was also alluding to an event commemorated that same week: the beginning of the beginning, 50 years earlier, when James D. Watson and Francis H. Crick revealed the structure of the DNA molecule itself. That, too, was an exciting time. Scientists knew that the molecule they were finally able to visualize contained nothing less than the secret of life, which permitted organisms to store themselves as a set of blueprints and convert this stored information back into live metabolism. In subsequent years, attempts to figure out how this conversion took place captivated the scientific world. DNA's alphabet was known to consist of only four types of nucleotide. So the information encoded in the double helix had to be decoded according to some rules to tell cells which of 20 amino acids to string together to constitute the thousands of proteins that make up billions of life-forms. Indeed, the entire living world had to be perpetually engaged in frenetic decryption, as eggs hatched, seeds germinated, fungus spread and bacteria divided.

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