On-line Ed Kit

Unlocking the Mysteries of Health and Disease

DNA contains instructions for everything our cells do, from conception until death. Studying the human genome all the DNA in our cells allows us to explore fundamental details about ourselves. The Human Genome Project, the international quest to understand the genomes of humans and other organisms, will shed light on a wide range of basic questions, like how many genes we have, how cells work, how living things evolved, how single cells develop into complex creatures, and what exactly happens when we become ill. Besides answering innumerable questions about our molecular selves, a deeper understanding of the fundamental mechanisms of life promises to lead to an era of molecular medicine, with precise new ways to prevent, diagnose and treat disease. The Human Genome Project (HGP) began in the United States in 1990, when the National Institutes of Health and the Department of Energy joined forces with international partners to decipher the massive amount of information contained in our genomes. The HGP began with a set of ambitious goals but has exceeded nearly all of its targets. Frequently ahead of schedule, HGP scientists have produced an increasingly detailed series of maps that help geneticists navigate through human DNA. They have mapped and sequenced the genomes of important experimental organisms. They completed a working draft covering 90 percent of the genome in 2000, and by 2003, they will finish the sequence with an accuracy greater than 99.99 percent fewer than one mistake every 10,000 letters. The HGP began transforming biology as soon as it started, because the information it generates has been disseminated rapidly through unrestricted, public databases. That information fuels today's heady pace of discoveries into the genetic basis of a wide range of disorders. These include diseases caused by changes in single genes to more common diseases like cancer, Alzheimer disease, diabetes, and heart disease where several genes in interaction with environmental factors influence who develops a disease and when.

Gene Discovery

Connecting a gene with a disease was a slow, arduous, painstaking, and frequently imprecise process before the advent of the HGP. In 1989, geneticists had tracked down only four genes associated with disease by sorting through heredity. By 1998, the same list included more than 100 genes. Consider two gene hunts, eight years apart: in 1989, scientists found the gene for cystic fibrosis after a 9-year search; eight years later, a gene for Parkinson disease was mapped in only 9 days, and precisely described within 9 months.

With more and more DNA sequence deposited in electronic databases, researchers spend less time collecting data with their own experiments and more time analyzing the wealth of data available to them. They can electronically scan long stretches of DNA to find genes in the sequence that may be responsible for a particular disease. Those are called candidate genes. If a candidate gene actually does play a role in a disease, it should be spelled differently in people with the disease compared to those without it; the alteration in spelling somehow disrupts the normal function of the gene product. For example, rare cases of early-onset Parkinson disease can result from a change in just one DNA letter, which in turn, changes one of the 140 amino acids that make up a key protein.

The gigabytes of DNA sequence data flowing from the HGP and the pro- gressively more detailed catalog of human sequence variations are helping scientists study increasingly complex genetic questions. Instead of restricting their studies to conditions caused by mutations in single genes, scientists can now study the genetic basis for complex diseases, like diabetes and Alzheimer disease, that involve several genes.











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