Scientists identify marks of differences between human and chimp genomes

Washington, Nov 6 : A team of researchers have carried out the largest study of differences between human and chimpanzee genomes, identifying regions that have been duplicated or lost during evolution of the two lineages.

The study is the first to compare many human and chimpanzee genomes in the same fashion.

The team show that particular types of genes - such as those involved in the inflammatory response and in control of cell proliferation - are more commonly involved in gain or loss.

They also provide new evidence for a gene that has been associated with susceptibility to infection by HIV.

"This is the first study of this scale, comparing directly the genomes of many humans and chimpanzees," said Dr Richard Redon, from the Wellcome Trust Sanger Institute, a leading author of the study.

"By looking at only one 'reference' sequence for human or chimpanzee, as has been done previously, it is not possible to tell which differences occur only among individual chimpanzees or humans and which are differences between the two species," he added.

"This is our first view of those two important legacies of evolution," he further added.

Rather than examining single-letter differences in the genomes (so-called SNPs), the researchers looked at copy number variation (CNV) - the gain or loss of regions of DNA.

CNVs can affect many genes at once and their significance has only been fully appreciated within the last two years.

The team looked at genomes of 30 chimpanzees and 30 humans: a direct comparison of this scale or type has not been carried out before.

The comparison uncovered CNVs that are present in both species as well as copy number differences (CNDs) between the two species.

CNDs are likely to include genes that have influenced evolution of each species since humans and chimpanzees diverged some six million years ago.

"Broadly, the two genomes have similar patterns and levels of CNVs - around 70-80 in each individual - of which nearly half occur in the same regions of the two species' genomes," said Dr Redon.

"But, beyond that similarity, we were able to find intriguing evidence for key sets of genes that differ between us and our nearest relative," he added.

According to Dr George Perry from Arizona State University, "It is evident that there has been striking turnover in gene content between humans and chimpanzees, and some of these changes may have resulted from exceptional selection pressures."

ANI