"The new study shows big differences in the genomes of humans and great apes within duplicated sequences containing rapidly evolving genes. Most of these differences occurred at a time just prior to the speciation of chimpanzees, gorillas, and humans," said University of Washington (UW) researchers Tomas Marques-Bonet and Jeffrey M. Kidd who headed the study.
"It is unclear why, but the common ancestor of humans, chimps and gorillas had an unusual activity of duplication," said Kidd. "Moreover, we don't yet know the functions of most of the genes that were affected by these duplications," he added.
The great ape ancestors, from whom humans, gorillas and chimps descended, lived in Africa between 8 million and 12 million years ago.
Most scientists think that the lineage that eventually led to chimps and humans diverged from the African great ape ancestors about 5 million to 7 million years ago.
"What's exciting for us to learn was that sequence duplication acceleration occurred in an era when other types of mutations had slowed within the hominid (human-like) lineage," said Evan Eichler, UW professor of genome sciences.
"There was significant increase in genome activity in both the number of duplication events and the number of base pairs of DNA that were affected," Marques-Bonet noted.
The results suggest that evolutionary properties of copy-number mutations, such as repeated segments, differ from other forms of mutations.
To understand the pattern and rate of genomic duplication during evolution, the researchers constructed a map of segmental duplications for four primate genomes: macaque, orangutan, chimpanzee, and human.
They then compared the duplications across the four species. They characterized a duplication as shared if it occurred in two or more of the four species and lineage-specific if it was found in just one species.
A small fraction of the duplicated content was human-specific, while the major part of duplications was shared with the other species.
According to the researchers, "Our team found striking examples of recurrent duplications of DNA segments that happened independently in different lineages."
"Most of the shared duplications were already present in the chimp-human common ancestor, but these are highly variable in copy number between and within human and great ape species," they added. (ANI)