Breaking the Code.

In a milestone that rival's man's first steps on the moon, President Bill Clinton announced last June the culmination of the first phase of the Human Genome Project. The ongoing 10-year-long research mission involves thousands of scientists worldwide. Their historic feat: a master "map" detailing the exact order of the 3.5 billion chemical units (made up of four different bases called nucleic acids) that compose your genetic code--hereditary information that determines all physical and many personality traits. "This map will revolutionize our understanding of human life," says James Pierce, a genetics professor at the University of the Sciences in Philadelphia, Pa.

The project's first goal was to locate the estimated 35,000 to 120,000 genes, or chemical instructions (see diagram) embedded in a coiled molecule of DNA (deoxyribonucleic acid). Since the billions of bases that combine to form genes are like an endless string of unpunctuated letters, scientists struggle to find where genes begin and end on a ribbon of DNA.

But they do know that each gene instructs a cell how to make a specific protein to build bones or fight infections, for example. "The genome will ultimately help us prevent and treat diseases linked to faulty genes, like cancer and obesity," Pierce says.

Phase two of the Human Genome Project--deciphering how genes function and interact to trigger diseases--could take many decades to complete. So far, about 7,000 genes have been identified, including genes linked to mental retardation in girls and obesity.

* Want to keep tabs on the project's progress? Check out this Web site sponsored by the U.S. Department of Energy: www.ornl.gov/hgmis