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Duplicons and Big Brains

Some dogged scientists suspect that a series of bursts of swift genetic changes may have been responsible for some critical moments in the human evolutionary story and may offer insights into the development of the large human brain, Emily Singer writes in Quanta magazine.

University of Washington geneticist Evan Eichler, for example, has been digging around in human and ape genomes for years focused on duplicated gene segments that spread across the genomes of the ancestors of humans and great apes some eight million to 12 million years ago, around the times the human line split off.

The particular patterns of duplicons that intrigue Eichler are found only in great apes and humans.

"I think it's a missing piece of human evolution," he tells Singer. "My feeling is that these duplication blocks have been the substrate for the birth of new genes."

Eichler and his team have used new analytical methods to discover that these duplicated regions in great apes are very active in producing RNA and proteins, which suggests that they have an important function.

But discovering what those functions may be is proving challenging, though enticing.

"Because these regions are so complex, they are often ignored by conventional genome studies, and some regions still haven't been fully sequenced," adds James Sikela, a geneticist at the University of Colorado School of Medicine. "So not only are they important, they are unfortunately unexamined."

Eichler is on the problem, Singer writes. He and a group at Scripps Research Institute have shown that a gene called SRGAP2C, which rode along as a core duplication and was spread among human ancestors, can affect how neurons develop and can trigger the development of a dense array of neuronal structures.

"I'm not saying it's responsible for the expansion of the human brain, but it might play a role in getting neural precursors in the right place," Eichler adds.

Additionally, Sikela and his group have been looking at a genetic component found in a family of genes in humans and other great apes, DUF1220, which appears to be involved in brain size. The more DUF1220 copies someone has, the research found, the larger their gray matter, Singer writes.