'Book of life' promises great strides for 21st century medicine

With the announcement that the entire human genetic code has been assembled, scientists now have a thrilling ''to do'' list for the 21st century.

The information could be used to cure cancer, Alzheimer's disease or diabetes. It could give patients valuable information about their susceptibility to heart disease, schizophrenia or high blood pressure. It could reveal in detail how an adult human being arises from a single cell, functions through a lifetime and dies.

But it will take years, even decades, before such dreams become reality.

''It's the end of the beginning,'' Human Genome Project director Francis Collins said Monday at a White House briefing. ''Together we must develop the advances in medicine that are the real reason for doing this work.''

The genes have not actually been decoded but entered, letter by letter, into an enormous computer database. The public effort headed by Collins has mapped 97 percent of the human genome and thoroughly covered, or sequenced, 85 percent. A for-profit rival, Celera Genomics of Rockville, Md., also announced Monday that it has completed 99 percent of the genetic sequence. Celera began its work last fall, using an approach that turned out to be faster than conventional methods.

The announcements mark a significant watershed in biology.

''Today we celebrate the revelation of the first draft of the book of human life,'' Collins said.

Scientists involved in both projects intend to publish their results jointly later this year. ''I think it's significantly more important than walking on the moon,'' said Jennifer Nyborg, a professor at Colorado State University who studies leukemia.

The goal of both teams is to identify and place into proper order the 3.12 billion chemical base pairs present in human DNA and to identify within that DNA the thousands of human genes. The base pairs are made up of four types of nucleotides, called adenine, thymine, cytosine and guanine. They are abbreviated A, T, C and G in the scientific description of the genome.

It is the order and sequence of these bases within the 23 pairs of human chromosomes that make up the genetic code.

J. Craig Venter, chief scientist of Celera Genomics, said the genomes of three females and two males who identified themselves as Hispanic, Asian, Caucasian or African-American have been sequenced.

In the near term, the new information is expected to revolutionize drug development, making it much easier for pharmaceutical companies to target their products at the actual causes of disease. Today, most drugs are developed by a trial-and-error method that simply throws thousands of compounds at a biochemical problem until one fixes it.

Researchers are also pursuing gene therapy, which would replace or supplement defective genes with correct copies. The field has suffered several recent setbacks, including the death of a patient last year during experimental treatment. Researchers have also found it difficult to find an efficient way to deliver corrected genes to cells where they are needed; they remain optimistic that effective methods will be found.