The genomic analyses also showed that humans and chimps appear to have accumulated more potentially deleterious mutations in their genomes over the course of evolution than have mice, rats and other rodents. While such mutations can cause diseases that may erode a species' overall fitness, they may have also made primates more adaptable to rapid environmental changes and enabled them to achieve unique evolutionary adaptations, researchers said.
Despite the many similarities found between human and chimp genomes, the researchers emphasized that important differences exist between the two species. About 35 million DNA base pairs differ between the shared portions of the two genomes, each of which, like most mammalian genomes, contains about 3 billion base pairs. In addition, there are another 5 million sites that differ because of an insertion or deletion in one of the lineages, along with a much smaller number of chromosomal rearrangements. Most of these differences lie in what is believed to be DNA of little or no function. However, as many as 3 million of the differences may lie in crucial protein-coding genes or other functional areas of the genome.
"As the sequences of other mammals and primates emerge in the next couple of years, we will be able to determine what DNA sequence changes are specific to the human lineage. The genetic changes that distinguish humans from chimps will likely be a very small fraction of this set," said the study's lead author, Tarjei S. Mikkelsen of the Broad Institute of MIT and Harvard. Among the genetic changes that researchers will be looking for a
Contact: Geoff Spencer
NIH/National Human Genome Research Institute