Did burst of gene duplication trigger human evolution

February 12th, 2009 - 5:02 pm ICT by IANS  

Washington, Feb 12 (IANS) Nearly 10 million years ago, segments of DNA in the genome of a common ancestor of humans, gorillas and chimpanzees began to duplicate copies at a greater rate than in the past, contributing to diseases like autism and schizophrenia.
But that gene duplication also may be responsible for a genetic flexibility that has resulted in some uniquely human characteristics.

“Because of the architecture of the human genome, genetic material is constantly being added and deleted in certain regions,” says Howard Hughes Medical Institute investigator and geneticist Evan Eichler, who led the project that uncovered the new findings.

“These are really like volcanoes in the genome, blowing out pieces of DNA,” he added.

Eichler and his colleagues focused on the genomes of four different species: macaques, orangutans, chimpanzees, and humans. All are descended from a single ancestral species that lived about 25 million years ago.

The line leading to macaques broke off first, so that macaques are the most distantly related to humans in evolutionary terms. Orangutans, chimpanzees, and humans share a common ancestor that lived 12-16 million years ago. Chimps and humans are descended from a common ancestral species that lived about 6 million years ago.

By comparing the DNA sequences of the four species, Eichler and his colleagues identified gene duplications in the lineages leading to these species since they shared a common ancestor.

They also were able to estimate when a duplication occurred from the number of species sharing that duplication. For example, a duplication observed in orangutan, chimpanzees, and humans but not in macaques must have occurred sometime after 25 million years ago but before the orangutan lineage branched off.

Eichler’s research team found an especially high rate of duplications in the ancestral species leading to chimps and humans, even though other mutational processes, such as changes in single DNA letters, were slowing down during this period, said a Howard release.

“There’s a big burst of activity that happens where genomes are suddenly rearranged and changed,” he says. Surprisingly, the rate of duplications slowed down again after the lineages leading to humans and to chimpanzees diverged.

“You might like to think that humans are special because we have more duplications than did earlier species,” he says, “but that’s not the case.”

These findings were published in the latest issue of Nature.

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