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Genome Sequences Launch a New Level of Scientific Challenges

Building a “Systems Level” View of Life
The DNA sequences generated in hundreds of genome projects now provide scientists with the “parts lists” containing instructions for how an organism builds, operates, maintains, and reproduces itself while responding to various environmental conditions. But we still have very little knowledge of how cells use this information to “come alive.” The functions of most genes remain unknown. Nor do we understand how genes and the proteins they encode interact with each other and with the environment. If we are to realize the potential of the genome projects, with far-ranging applications to such diverse fields as medicine, energy, and the environment, we must obtain this new level of knowledge.

One of the greatest impacts of having whole-genome sequences and powerful new genomic technologies may be an entirely new approach to conducting biological research. In the past, researchers studied one or a few genes or proteins at a time. Because life doesn’t operate in such isolation, this inherently provided incomplete—and often inaccurate—views. Researchers now can approach questions systematically and on a much grander scale. They can study all the genes expressed in a particular environment or all the gene products in a specific tissue, organ, or tumor. Other analyses will focus on how tens of thousands of genes and proteins work together in interconnected networks to orchestrate the chemistry of life—a new field called “systems biology” (see “Genomes to Life”).

Charting Human Variation
Slight variations in our DNA sequences can have a major impact on whether or not we develop a disease and on our responses to such environmental factors as infectious microbes, toxins, and drugs. One of the most common types of sequence variation is the single nucleotide polymorphism (SNP). SNPs are sites in the human genome where individuals differ in their DNA sequence, often by a single base. For example, one person might have the DNA base A where another might have C, and so on. Scientists believe the human genome has at least 10 million SNPs, and they are generating different types of maps of these sites, which can occur both in genes and noncoding regions.

Sets of SNPs on the same chromosome are inherited in blocks (haplotypes). In 2002 a consortium of researchers from six countries established a 3-year effort to construct a map of the patterns of SNPs that occur across populations in Africa, Asia, and the United States. Researchers hope that dramatically decreasing the number of individual SNPs to be scanned will provide a shortcut for tracking down the DNA regions associated with common complex diseases such as cancer, heart disease, diabetes, and some forms of mental illness. The new map also may be useful in understanding how genetic variation contributes to responses to environmental factors.

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