A Missing Genetic Link in Human Evolution

Mysterious episodes of genetic duplication in our great ape ancestors may have paved the way for human evolution

By Emily Singer and Quanta Magazine

SRGAP2: Whereas chimps and orangutans have only one, humans have multiple copies of the gene SRGAP2 which is believed to be involved in the development of the brain. Image: Dennis/Cell/Quanta

From Quanta Magazine (find original story here).

About 8 million to 12 million years ago, the ancestor of great apes, including humans, underwent a dramatic genetic change. Small pieces of DNA replicated and spread across their resident chromosomes like dandelions across a lawn. But as these dandelion seeds dispersed, they carried some grass and daisy seeds additional segments of DNA along for the ride. This unusual pattern, repeated in different parts of the genome, is found only in great apes bonobos, chimpanzees, gorillas and humans.

I think its a missing piece of human evolution, said Evan Eichler, a geneticist at the University of Washington, in Seattle. My feeling is that these duplication blocks have been the substrate for the birth of new genes.

Over the past few years, scientists have begun to uncover the function of a handful of genes that reside in these regions; they seem to play an important role in the brain, linked to the growth of new cells, as well as brain size and development. In September, Eichlers team published a new technique for analyzing how these genes vary from person to person, which could shed more light on their function.

Much about the duplication process and its implications remains a mystery. Eichler and others dont know what spurred the initial rounds of duplications or how these regions, dubbed core duplicons, reproduced and moved around the genome.

Despite the duplication-linked genes potential importance in human evolution, most have not been extensively analyzed. The repetitive structure of the duplicated regions makes them particularly difficult to study using standard genetic approaches the most efficient methods for sequencing DNA start by chopping up the genome, reading the sequence of the small chunks and then assembling those sections like one would a puzzle. Trying to assemble repetitive sections is like trying to put together a puzzle made of pieces with almost the same pattern.

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A Missing Genetic Link in Human Evolution