After trolling through sequence data for nine very different organisms, scientists have discovered that genes are copied far more frequently than previously thought. The study, published in the 10 November issue of Science, suggests that some duplicate genes play a key role in the evolution of new traits and in speciation.
Most evolutionary biologists believe that genomes grow and diversify by gene duplication. The idea is that when genes are accidentally copied twice, the "extra" copies can take on a new function, for instance by turning on at a different time in development or in a different tissue. Yet until recently, researchers didn't have much to back up this theory.
A rich source for evidence, evolutionary biologist Michael Lynch and computer scientist John Conery of the University of Oregon, Eugene, realized, is the recent flurry of genome sequencing data. The duo used a computer program to find duplicate genes in the genomes of the fruit fly, yeast, and nematode, and among all the protein-coding sequences available for the mouse, chicken, human, rice, and the plant Arabidopsis thaliana.
The two found an "astronomical rate of gene duplication," says Sally Otto, an evolutionary biologist at the University of British Columbia in Vancouver, Canada. In fact, duplications occur as often as single-base changes within genes, which have long been considered the primary means by which genomes evolve. "Gene duplications are so frequent that we really need to take them into account as an important source of genetic variation," says Andreas Wagner, an evolutionary biologist at the University of New Mexico, Albuquerque, and the Santa Fe Institute.
Several researchers question how Lynch came up with his pool of duplicate genes and worry about some of the resulting estimates. Manyuan Long, an evolutionary biologist at the University of Chicago, thinks that Lynch's analysis doesn't adequately take into account long-lived gene copies, many of which also exist in these genomes. Nevertheless, the report is "a very nice example of how the creative analyses of genomic databases can provide valuable but previously inaccessible information about evolution," says Loren Rieseberg, an evolutionary biologist at Indiana University, Bloomington.