PARIS (AFP) — Lab sleuths said they had laid bare the complete genetic code of a family of fruitflies, enabling the world's first comparison of the genomes of a dozen closely-related species.
The achievement opens a window onto key evolutionary processes and may one day serve as a model for understanding why we humans and our nearest primate cousins are so close yet also so different, they believe.
In studies to be published on Thursday in the British journal Nature, around 150 scientists around the globe added 10 fully-sequenced genomes of the fruitfly Drosophila to two that had already been decoded.
They also began to mine the treasure trove of data, publishing analyses touching on two cornerstones of evolutionary theory -- the principles of positive and negative selection.
Positive selection means genetic mutations that spread through a species because they provide an advantage in the struggle to survive. Negative selection means genetic characteristics that are forced out of a species because they are an encumbrance to survival.
By looking across a broad family, researchers can spot a mutation that has been favoured as it confers an evolutionary advantage on a specific species -- such as a change in the immune system -- or a mutation that has been weeded out.
They can also identify genetic code that has remained unchanged, or conserved, because of its enduring usefulness to the species.
Histone proteins, which determine how DNA is packed inside cell nuclei, have barely changed over the 60 million years going back to the single common ancestor from which all the Drosophila species eventually emerged, the investigators found.
"Once evolution figures how to make something like that work, it does not change easily," said David Rand of Brown University, whose laboratory worked on sequencing mitochondrial DNA from all 12 fruitfly genomes.
Only 77 percent of the approximately 13,700 protein-coding genes are shared by all 12 species, the consortium says.
The humble fruitfly, especially the main species, Drosophila melanogaster, has long been used to probe the biology of multicellular organisms.
It is familiar to many as the barely visible objects of school-age experiments on the mechanics of heredity.
Over the last decade, however, geneticists have gradually shunted the harmless flies aside in favor of worms and especially mice, which offer better models for studying the relationship between genes and human disease.
But the newly sequenced "Drosophila Dozen," which range from the tiny D. simulans to the relatively giant D. grimshawi of Hawaii and the red-eyed D. yakuba of the African savannah, are sure to rekindle interest in the winged beasts.
"The 12 Drosophila genomes give us an unprecedented opportunity to understand evolutionary adaptation right down at the genetic level," said Brown researcher Kristi Montooth.
"If we want to understand how the fly that lives on the savannah is different from the fly that lives in the desert, we can trace physiological differences back to specific genes."
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