Chimp DNA sheds light on humans
2005-09-01 07:00
Paris - Scientists on Wednesday unveiled the genetic code of the chimpanzee, showing that humans are biologically distinct from apes thanks to a small handful of important differences in DNA.
The first genome to be sequenced of an animal primate reveals that the chimpanzee has about three billion base pairs, the "rungs" of DNA code that provide the chemical recipe for life.
The tally for Pan troglodytes is largely the same as for Homo sapiens, and indeed for those other mammal species that have been sequenced so far.
Of the chimp's three thousand million base pairs, a mere 35 million of them - less than four percent - are different from a human's.
Yet these scant differences have a huge impact.
They have given us an outsized brain, the ability to walk upright on two feet, develop complex language skills, adapt quickly to changing environments, as well as other uniquely human features.
"To put this into perspective... the number of genetic differences between a human and a chimp is about 10 times more than between any two humans," the US National Institutes of Health (NIH), which helped fund the research, noted.
Humans and chimps have a common ancestor, an apelike creature who last walked the Earth around six million years ago.
'Tiny but significant ways'
The march of time has sculpted the ape and human genomes in tiny but significant ways, according to an analysis published alongside the landmark draft sequence in Thursday's issue of Nature, the British weekly science journal.
Most of the differences between humans and chimps lie in stretches of DNA that appear to have little or no function.
But as many as three million base pairs differ in functional areas, including genes, the protein-making "nuggets" in the DNA goldmine.
Fifty-three genes present in the human genome are missing or partially deleted from the chimp genome - so the next challenge is to see what, specifically, these genes do. Could they explain why we are human?
Just as intriguing are genes that are present in the chimp but which, for some reason, have disappeared in humans. For instance, one ape gene, caspase-12, produces an enzyme that appears to protect the animal from Alzheimer's disease, but which does not exist in modern humans.
"As our closest living evolutionary relatives, chimpanzees are especially suited to teach us about ourselves," said a lead author, Robert Waterston of the University of Washington School of Medicine in Seattle.
"This genomic comparison dramatically narrows the search for the key biological differences between the species."
The human genome was published in draft form in February 2001 in a race between two rival teams of scientists. It was followed by the mouse (December 2002) and rat (March 2004).
Other organisms whose genetic code has been unravelled include a small earthworm called the nematode; the fruitfly; and yeast. Like the mouse and rat, these are fundamental tools in lab research.