12 December 2003
ByAppeared in BioNews 238
US scientists have unveiled the entire genetic code of our closest animal relative, the chimpanzee. Teams at the Massachusetts Institute of Technology in Boston and the Washington University School of Medicine took less than a year to churn through the three billion DNA base-pairs (chemical letters) that make up the sequence. Around 99.2 per cent of it is identical to the human genome, but, according to a separate study, there are key differences in genes involved in smell and hearing.
Researchers first proposed sequencing the chimp genome three years ago, because they believed it would be a good way to identify genetic differences that are uniquely human. Also, comparing human and chimp genes could help scientists better understand diseases such as Alzheimer's disease, malaria and AIDS, which affect only humans.
The draft version of the chimp's genetic make-up, which is around 90 per cent complete, is now freely available via the Internet, aligned with its human counterpart. 'We want to let the scientific community know that the sequence is available and they can have access to it, said team leader Richard K Wilson. Detailed comparisons of the human and chimp genomes will be published in the next few months, he promised, saying 'it's a nice first glimpse, but there's more to come.'
Another US team, based at the biotech company Celera Diagnostics in Alameda, California, has already compared around 7,500 chimp and human genes with those of the mouse. The results, published in the journal Science, reveal some of the genetic differences between the two primate species, which have arisen since they shared their last common ancestor five million years ago. All DNA sequences change over time, as mistakes are made when DNA is copied and passed on from one generation to the next. The researchers wanted to identify those that have differed most between chimps and humans, since their earlier shared ancestor, the mouse.
They found differences in human genes linked to smell, many of which looked in danger of becoming redundant. This probably reflects the lesser importance of smell in our modern lifestyles compared to that of chimpanzees, reports Nature. The team also found differences in 21 genes linked to hearing, which could be to do with language, speculates geneticist Svante Paabo. Around 80 genes that make proteins involved in digestion also differ between chimps and humans, which could reflect changes in diet.
However, some scientists warn that there are so few genetic differences between humans and chimps that some may be due to chance, rather than evolution. 'My gut feeling is that there isn't enough data here', said evolutionary biologist Adam Eyre-Walker, who thinks it would be better to combine the results from many genes. And Michele Cargill of Celera Diagnostics cautioned that although her group's study could pinpoint the types of genes important in human differences, 'just finding a change in one protein gives us no idea of how it affects the whole animal'.