The #1 source for news about monkeys and apes

[Josh Greenman <joshg1973 AT yahoo.com>]

http://www.newscientist.com/news/print.jsp?id=ns99995044

Chromosomes reveal surprise human-chimp differences

18:00 26 May 04

Humans and their closest relatives, chimpanzees, may be more different 
than geneticists have realised.

 Previously, scientists have estimated that humans and chimps differ in 
about 1.5 per cent of the DNA letters that spell out their genomes. 
However, these estimates have been based on studies of only small 
subsets of the two genomes, because the chimp genome has not been 
sequenced precisely enough to allow a large-scale, base-by-base 
comparison.

That has now changed, thanks to the International Chimpanzee Chromosome 
22 consortium, a team of researchers based in Asia and Europe that has 
sequenced a single chimpanzee chromosome in unprecedented detail.

 The group then compared this sequence against its human counterpart, 
chromosome 21. They found that the two differ at only 1.44 per cent of 
the DNA bases that the two chromosomes have in common - a minuscule 
difference that confirms earlier estimates.

 However, each gene contains hundreds or thousands of bases. This means 
even the tiny difference seen is enough to change the amino acid 
sequence of 83 per cent of the proteins generated by the 231 genes on 
the chromosome.

 Lost and found

"Simple math probably says the 80 per cent is not surprising," says 
Asao Fujiyama, a consortium member at the Japanese National Institute 
of Informatics in Tokyo. Also, because most of these proteins differ by 
only a handful of amino acids, they should still be very similar in 
function.

 However, the group also found nearly 68,000 places where genetic 
material -usually just a few bases - had been gained or lost in one of 
the species. These changes were enough to cause major differences in 
the structure of over 20 per cent of the proteins - a much larger 
difference than previously suspected.

 "Since chimps are our closest kin, we thought that protein structures 
would be highly conserved," says Fujiyama. It is not yet clear, though, 
how these changes help explain the unique biology of humans.

 "We don't have a good understanding of how much of the difference 
really matters to what makes us human," says Tarjei Mikkelsen, a 
bioinformaticist at the Broad Institute in Cambridge, Massachusetts, 
who is involved in analysing the chimpanzee genome.

Journal reference: Nature (vol 429, p 382)