the map of life.

What makes you you? It's in your genes--and scientists are racing to decipher them!

You and your friends may not realize it, but you probably sit around and gab a lot about genes.

"I'd give my straight blonde hair any day for Michelle's wild red curls."

"I wouldn't mind being as tall as Josh, or as good a basketball player."

"Who gave Lateesha the right to have those stunning brown eyes?"

That's right, genes--the hereditary material embedded in every cell of your body that determines your height, hair and eye color, the shape of your head and nose. They even impact how you deal with stress, how you'll age, and what diseases you're susceptible to.

In fact, it's devastating diseases like cancer--and the desperate search for treatments--that have sparked the most monumental undertaking in science history: the Human Genome Project (HGP).

In 1990, an international group of universities and laboratories led by the U.S. National Institutes of Health and the Department of Energy embarked on a 15-year mission to construct a detailed map of the human genome, or the entire DNA molecule that instructs cells how to make a human being.

Today, more than halfway through the project, researchers have thoroughly sequenced only 4 to 7 percent of the genome. But last year a few private enterprises, eager to reap a fortune by patenting human genes for medical uses, jump-started fierce competition. One company even claims it can map the entire human genome by 2001 (see timeline, p. 10).

TOTAL BODY MANUAL

Think of the genome as the most complex instruction manual ever conceived on how and why your body works except scientists don't know how to read most of it yet.

Your body is composed of 10,000 trillion cells. Every single cell--whether in your toenail, underarm hair, bone, or blood--houses a complete DNA molecule (see miniposter, p. 12). That sole molecule of DNA contains every piece of information your body needs to function in thousands of ways--from growing limbs to fighting colds.

In turn, each DNA molecule consists of two long, coiled strands. The strands are made up of only four chemicals, called bases: adenine (A), thymine (T), guanine (G), and cytosine (C). Amazingly, the bases pair up in just two ways to hold the strands together--A with T, and G with C. Yet they link together to form 3 billion base pairs in one DNA!

Scientists now know that in the precise order or sequence of these base letters lies every specific instruction contained in your "map of life."

ENTER GENES

The instructions in a DNA molecule that tell cells how to build muscles, create eye color, or ward off diseases, are called genes. What still baffles genome researchers is that genes make up only a tiny fraction of the DNA molecule--about 3 percent of the 3 billion base pairs in DNA. What about the other 97 percent?

Scientists call it noncoding DNA, made mostly of the same letter sequences repeated over and over again. They still don't have the foggiest idea what noncoding DNA is all about. But scientists do know that even one missing letter or misspelled "word" in the entire thread of the DNA instruction manual can spell deafness, obesity, or mental retardation, for example. In other words, the faulty letter, or genetic defect, might be either part of a gene or the noncoding DNA--researchers don't yet know for sure. That's why it's so critical for them to decode the exact and entire sequence of the human genome.

It's no easy task. Consider this: If you were to write out the entire human DNA sequence, the letters would fill 200 volumes the size of a 1,000-page phone directory.

To tackle the job of deciphering DNA, HGP researchers first took DNA samples from a small group of anonymous volunteers. (The DNA of every person on Earth is 99.9 percent identical. The 0.1 percent is what makes each of us unique!) They then divided the work into two stages--mapping and sequencing.

Genome scientist Elaine Mardis at Washington University in St. Louis, Missouri, offers this analogy: Picture a road atlas of the United States. "Mapping the genome is like charting where every highway leads to and where every town is." Sequencing, she explains, means pinpointing the location of every street and house in the U.S.

Scientists completed the mapping phase, which involved marking off 50,000 chemical "signposts" along the DNA chain, in 1996. Now they're sequencing, or finding out the exact order of base letters in the areas between the signposts. They'll finish this part of the project in 2003.

WHAT'S NEXT?

Though the Human Genome Project may seem light years from its goal, researchers around the globe have already reaped its benefits. Every night HGP scientists post their latest genome sequences on the Internet. Every day thousands of researchers access that information.

Doctors and researchers pore through the completed sequences and use them as a resource to locate and identify specific genes, especially those that cause diseases. So far, scientists from universities and labs around the world have identified about 300 disease genes, including those that play a role in epilepsy, Parkinson's disease, breast and colon cancer, and even heroin addiction.

Genome researcher Tom Hudson at the Massachusetts Institute of Technology is in hot pursuit of the genes that cause asthma, a respiratory disease currently on the rise in the U.S. Identifying a disease gene, he says, is critical for researchers to solve basic riddles: What does the gene do? What factors switch it on? What would it take to switch the gene off and render it powerless to cause disease?

"If we can understand the process that goes wrong, we can find new and better medication," Hudson says. And by detecting defective genes before the onset of devastating diseases, doctors can help patients take preventive measures.

Says Hudson, "There are unlimited benefits to be had from the genome project."