A partial, duplicated copy of a gene appears to be responsible for the critical features of the human brain that distinguish us from our closest primate kin. The momentous gene duplication event occurred about two or three million years ago, at a critical transition in the evolution of the human lineage, according to a pair of studies published on May 3, 2012 in Cell. The studies are the first to explore the evolutionary history and function of any uniquely human gene duplicate. These "extra" genes are of special interest as they provide likely sources of raw material for adaptive evolutionary change. Until now, studying them has been a technical challenge because they are nearly indistinguishable from each other. "There are approximately 30 genes that were selectively duplicated in humans," said Dr. Franck Polleux, an expert in brain development at The Scripps Research Institute. "These are some of our most recent genomic innovations." Intriguingly, many of these genes appear to play some role in the developing brain. In two independent studies, Dr. Polleux and Dr. Evan Eichler, a genome scientist at the University of Washington, focused their expertise and attention on one of the genes known as SRGAP2. This gene has, in fact, been duplicated at least twice during the course of human evolution, first about 3.5 million years ago and then again about 2.5 million years ago. The new work shows that the second and relatively recent duplication event produced only a partial copy of the gene. This copy acts at exactly the same time and place as the original, allowing it to interact with and block the ancestral gene's function. "This innovation couldn't have happened without that incomplete duplication," Dr. Eichler said.
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