BIOLOGISTS have broken the genetic code. They've read some of the instructions that determine the composition of simple organisms. They've altered a few plants and bacteria. Now some of them are after a far bigger prize - the human genome. The genome is the entire 3 billion-letter ``text'' that contains the genetic instructions for the formation of human beings. That's roughly the number of letters in three year's run of a major seven-day-a-week metropolitan newspaper. So far, the longest such ``text'' the biologists have read is the 172,000-letter sequence of the Epstein-Barr virus - less than 10 percent of a single newspaper issue, using the analogy above. An intensive, dedicated project to go from that to getting the complete sequence of the human genome's 3 billion letters would be the most ambitious single effort biologists have ever undertaken.
Cost estimates run between several hundred million and $1 billion. It probably would take 10 to 20 years to complete. This would catapult biologists - who are used to working in small groups on small programs - into the realm of ``big science.'' It would be for them what building a particle accelerator is for physicists or orbiting the Hubble space telescope is for astronomers - a prospect some biologists view with trepidation.
As momentum builds toward organizing such a project, there is sharp debate among biologists about the wisdom for rushing ahead.
For Walter Gilbert of Harvard University, a dedicated effort to sequence the human genome would be ``like pursuing the Holy Grail.'' The Nobel Prize winning microbiologist says it would create the biological equivalent of the Rosetta stone - ``a complete library of information that biologists could search'' to find the genetic instructions for making a human being. It would be a major aid in understanding gene-linked diseases and developing medical treatments for them. It also should aid in developing many new drugs based directly on chemicals the body uses naturally.