Scientists Reveal Genetic Mysteries of Fruit Fly




PITTSBURGH -- Opening a new window into the mysteries of animal design and the nature of life, biologists described Thursday how they had decoded almost the entire genetic rule book for making the Drosophila fruit fly, an organism whose study is interwoven with the progress of modern biology.


The achievement closes a cycle in scientific history that began in 1910, when Thomas Morgan of Columbia University chose Drosophila as the experimental animal with which he and his students would work out many of the basic principles of genetics.


The announcement Thursday is a milestone in the effort to sequence the human genome, because it seems to validate a high-risk decoding strategy adopted by Dr. J. Craig Venter of Celera Corp., which is competing against a public consortium of university centers to decode the human genetic inheritance.


Despite the rivalry in decoding the human genome, the work described in Pittsburgh was a collaboration between a team of scientists led by Venter and another led by Dr. Gerald Rubin, the University of California biologist who directs the consortium's work on the fly.


Celera reported in December that it had sequenced the fruit-fly genome. But the results are only now being made public, both in lectures given in Pittsburgh at the annual meeting of the world's fly biologists and in this Friday's issue of the journal Science.


"Because fly cell biology and development have much in common with mammals, this sequence may be the Rosetta stone for deciphering the human genome," two biologists not connected with the sequencing, Dr. Thomas Kornberg and Dr. Mark Krasnow, write in a commentary in Science. They call completion of the fly genome "a monumental technical feat."


Celera chose the fruit-fly genome as a pilot project for tackling the human genome, which is 30 times as large. The Celera approach with which the fly was sequenced involves assembling the genome from millions of small fragments in a single giant computation. The public consortium, by contrast, follows a more cautious strategy of collecting the small pieces into segments and then joining these into a complete genome.


Arriving for an afternoon session Thursday, 1,300 fly biologists at their annual meeting found on their chairs a gift from Celera, a CD-ROM of the genome sequence of their favorite organism. Venter was given a standing ovation after the president of the fly biologists' association, Dr. Gary Karpen of the Salk Institute, said of the Drosophila genome that "we are about to be handed an incredible tool that many of us only dreamed about for many years."


Borrowing from the language of computer programmers, the Venter-Rubin teams termed today's version of the fly genome "Release 1," meaning that perfected editions would be published in the future. At present there remain 1,299 gaps in the 120 million chemical units of DNA that have been decoded. The gaps are small and are expected to be closed within a few months.


One immediate surprise is that so few genetic instructions are required for the development and maintenance of a fly, compared with the number known to be needed by other organisms. The fruit fly is a complex miniature machine with elaborate behavior and a courtship ritual that fly experts say closely resembles the human variety. Yet the fruit fly has only twice as many genes as yeast, a single-celled fungus, and considerably fewer than the 18,425 of the C. elegans roundworm, the only other animal whose entire genome has been sequenced.


"This says you build complexity not by having more genes but by using them in more inventive ways," Rubin said.


Rubin said he interpreted the new genome data to mean people, with their predicted total of 80,000 genes, acquire their greater complexity from an elaborate arrangement of the same basic parts, resembling a fruit fly much as a supercomputer resembles a personal computer. "Once evolution got it right, it basically made minor tinkerings, he said, referring to 600 million years ago, when flies and people had a common ancestor.