Scientists have unveiled a completed version of the entire chimpanzee genome, after publishing a rough draft in December 2003. The international team, which reported its findings in the latest issue of Nature, says that chimps share 96 per cent of their genetic material with humans. And the DNA that makes up the actual genes of the two species is almost 99 per cent identical. The researchers hope the $25 million effort will help shed light on conditions such as Alzheimer's disease.
Chimps and humans last shared a common ancestor around six million years ago. The genomes of both are made up of around 2.8 billion 'base-pairs' - the chemical 'letters' of the DNA code. The latest study shows that about 35 million DNA base-pairs differ between the two genomes, and a further five million locations differ because stretches of DNA have been inserted or deleted during evolution. Many of these differences are thought to lie in parts of the genome that has no particular role, but around three million may affect genes, or areas responsible for switching genes on and off.
'The sequencing of the chimp genome is a historic achievement that is destined to lead to many more exciting discoveries with implications for human health', said Francis Collins, director of the US National Human Genome Research Institute. He added that it was becoming clear that comparing the human genome with that of other species is 'an enormously powerful tool for understanding our own biology'.
Most chimp and human genes make very similar proteins - almost a third are identical, with many others differing by just one amino acid (protein building block). However, interestingly, more than 50 genes present in humans are either partly or completely missing in chimps. They include three genes involved in inflammation, which could help explain key immune response differences between the two species. Conversely, humans have lost a working version of a gene called caspase-12, which makes a protein that may protect other animals against Alzheimer's disease.
The chimp joins humans, rats and mice as the fourth mammal to have its genetic code laid fully bare, although draft versions of the dog and cow genomes have also been completed. Chris Stringer, of London's Natural History Museum, said the publication of the chimp genome was 'timely', given the current growth of 'anti-evolutionary ideas' in the US. 'The genome will enable us to look at evolutionary processes', he told the Guardian newspaper, adding 'we need to know what changed, when, and what made it change'. The DNA used for the chimp genome project came from an animal called Clint, who died last year of heart failure at the relatively young age of 26.