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Introduction - The Human Genome Project


Since the beginning of time, people have yearned to explore the unknown, chart where they have been, and contemplate what they have found. The maps we make of these treks enable the next explorers to push ever farther the boundaries of our knowledge - about the earth, the sea, the sky, and indeed, ourselves. On a new quest to chart the innermost reaches of the human cell, scientists have now set out on biology's most important mapping expedition: the Human Genome Project. Its mission is to identify the full set of genetic instructions contained inside our cells and to read the complete text written in the language of the hereditary chemical DNA (deoxyribonucleic acid). As part of this international project, biologists, chemists, engineers, computer scientists, mathematicians, and other scientists will work together to plot out several types of biological maps that will enable researchers to find their way through the labyrinth of molecules that define the physical traits of a human being.

Packed tightly into nearly every one of the several trillion body cells is a complete copy of the human "genome" - all the genes that make up the master blueprint for building a man or woman. One hundred thousand or so genes sequestered inside the nucleus of each cell are parceled among the 46 sausage-shaped genetic structures known as chromosomes.

New maps developed through the Human Genome Project will enable researchers to pinpoint specific genes on our chromosomes. The most detailed map will allow scientists to decipher the genetic instructions encoded in the estimated 3 billion base pairs of nucleotide bases that make up human DNA. Analysis of this information, likely to continue throughout much of the 21st century, will revolutionize our understanding of how genes control the functions of the human body. This knowledge will provide new strategies to diagnose, treat, and possibly prevent human diseases. It will help explain the mysteries of embryonic development and give us important insights into our evolutionary past.

The development of gene-splicing techniques over the past 20 years has given scientists remarkable opportunities to understand the molecular basis of how a cell functions, not only in disease, but in everyday activities as well. Using these techniques, scientists have mapped out the genetic molecules, or genes, that control many life processes in common microorganisms. Continued improvement of these biotechniques has allowed researchers to begin to develop maps of human chromosomes, which contain many more times the amount of genetic information than those of microorganisms. Though still somewhat crude, these maps have led to the discovery of some important genes.

By the mid-1980s, rapid advances in chromosome mapping and other DNA techniques led many scientists to consider mapping all 46 chromosomes in the very large human genome. Detailed, standardized maps of all human chromosomes and knowledge about the nucleotide sequence of human DNA will enable scientists to find and study the genes involved in human diseases much more efficiently and rapidly than has ever been possible. This new effort - the Human Genome Project - is expected to take 15 years to complete and consists of two major components. The first - creating maps of the 23 pairs of chromosomes - should be completed in the first 5 to 10 years. The second component - sequencing the DNA contained in all the chromosomes - will probably require the full 15 years.

Although DNA sequencing technology has advanced rapidly over the past few years, it is still too slow and costly to use for sequencing even the amount of DNA contained in a single human chromosome. So while some genome project scientists are developing chromosome maps, others will be working to improve the efficiency and lower the cost of sequencing technology. Large-scale sequencing of the human genome will not begin until those new machines have been invented.

Why do the Human Genome Project?

Most inherited diseases are rare, but taken together, the more than 3,000 disorders known to result from single altered genes rob millions of healthy and productive lives. Today, little can be done to treat, let alone cure, most of these diseases. But having a gene in hand allows scientists to study its structure and characterize the molecular alterations, or mutations, that result in disease. Progress in understanding the causes of cancer, for example, has taken a leap forward by the recent discovery of cancer genes. The goal of the Human Genome Project is to provide scientists with powerful new tools to help them clear the research hurdles that now keep them from understanding the molecular essence of other tragic and devastating illnesses, such as schizophrenia, alcoholism, Alzheimer's disease, and manic depression.

Gene mutations probably play a role in many of today's most common diseases, such as heart disease, diabetes, immune system disorders, and birth defects. These diseases are believed to result from complex interactions between genes and environmental factors. When genes for diseases have been identified, scientists can study how specific environmental factors, such as food, drugs, or pollutants interact with those genes.

Once a gene is located on a chromosome and its DNA sequence worked out, scientists can then determine which protein the gene is responsible for making and find out what it does in the body. This is the first step in understanding the mechanism of a genetic disease and eventually conquering it. One day, it may be possible to treat genetic diseases by correcting errors in the gene itself, replacing its abnormal protein with a normal one, or by switching the faulty gene off.

Finally, Human Genome Project research will help solve one of the greatest mysteries of life: How does one fertilized egg "know" to give rise to so many different specialized cells, such as those making up muscles, brain, heart, eyes, skin, blood, and so on? For a human being or any organism to develop normally, a specific gene or sets of genes must be switched on in the right place in the body at exactly the right moment in development. Information generated by the Human Genome Project will shed light on how this intimate dance of gene activity is choreographed into the wide variety of organs and tissues that make up a human being.

Go to next story: Ethical issues of the Human Genome Project?

See Graphics Gallery: Comparative Scale of Mapping

See the Human Genome Program web site at the Department of Energy

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