In June of 2000, two teams of scientists announced jointly that they had each finished sequencing the human genome. This remarkable news made headlines all over the world because it meant that finally disease researchers would have a map with which to begin seeking cures for all kinds of genetic diseases. Almost as amazing was the fact that the two teams, one government-led and one privately owned, and pushed by the fierce competition between them, completed the sequencing five years ahead of schedule.

Their speedy progress was made possible, in part, by simply throwing more resources at the task, using more equipment, more people, and increased automation. At least that was the strategy taken by the government-led Human Genome Project. The private biotech firm Celera, however, changed the rules of the sequencing race -- and in doing so, revolutionized the science of genomics.

Celera boldly called their gene-sequencing method the "shotgun" technique. Here's how it worked: To decode the genome, each of the company's three hundred sequencers chopped up long strands of DNA into tiny segments and replicated them thousands of times inside bacteria. They stained the segments with fluorescent dyes so that each of the four types of nucleotides gave off a different color. Then they identified every nucleotide in a given sample. Since the process was automated, it could operate continuously twenty-four hours a day, seven days a week. But while the decoding process was efficient, it was also nearly completely random. That's because as the sequencers cut up and decoded segments of DNA, they did not keep track of the original location of each piece within the larger segment.

In fact, the news that fell below the June 2000 headlines was that Celera researchers hadn't really finished the sequencing process, at least not completely or accurately. At that time, Celera's machines had decoded the genome -- they had read every letter -- but those letters were not yet plotted on anything that resembled a genome map. Celera's method required another not-inconsequential step. And no one knew for sure how long this step might take.

A Celera supercomputer used a mathematical algorithm to reassemble the decoded genome. This machine compared thousands of segments of DNA at a a time in search of overlap among them. Overlap exists because the sequencers cut strands of DNA randomly, producing segments of different lengths and with different beginning and ending points. By comparing the codes of countless segments, Celera's computer painstakingly reassembled them like so many tiny pieces of a jigsaw puzzle. In February of 2001, eight months after the first announcement, Celera published the complete map of the human genome. The Human Genome Project, which began more than five years before Celera joined the sequencing race, published its human genome map in another journal the same week.