The #1 source for news about monkeys and apes

[Eric Brager <eric AT looney.com>]

http://www.alertnet.org/thenews/newsdesk/N26710546.htm

26 May 2004 16:59:44 GMT

By Maggie Fox, Health and Science Correspondent

WASHINGTON, May 26 (Reuters) - Tiny genetic changes add up to huge 
differences when human DNA is compared to that of chimpanzees, researchers 
said on Wednesday in a report that explains how people and apes can be so 
close, yet so far apart.

Genetically, chimpanzees are 98.5 percent identical to humans. But the 
differences between the species are clearly profound and geneticists have 
been laboring to find out how such subtle variations in DNA can be so 
important.

"Clearly, the genomic differences between humans and chimps are much more 
complicated than conventional wisdom has portrayed," Asao Fujiyama of the 
RIKEN Genomic Sciences Center in Yokohama, Japan, and colleagues in Japan, 
Taiwan and China wrote in their report, published in this week's issue of 
the journal Nature.

The comparison will help understand disease and also help in comparing one 
person's genetic sequence to another by helping to set a "base" genetic 
sequence that can be used to determine the individual human variations in 
DNA.

Fujiyama's team compared chromosome 22 on three different chimpanzees to 
its counterpart in humans, chromosome 21.

They looked for differences that would help separate the human sequence 
from the chimp sequence.

Fujiyama's team found just 1.44 percent of the DNA was different at the 
level of single letters of genetic code.

These letters, A, C, T and G, stand for the nucleotides that make up the 
DNA of all living creatures. The nucleotides match up to make amino acids, 
which in turn string together into genes that control the proteins made by 
cells.

There are vast stretches of DNA that do not make up genes and scientists 
are struggling to understand their importance.

Fujiyama's team found differences that may be more important than the 
single-letter changes.

BIG PROTEIN DIFFERENCES

"There is also an impressive number (68,000) of small to large stretches of 
DNA that have been either gained or lost (these are called 'insertions or 
deletions', 'indels' for short) in one species or the other," the 
researchers wrote.

"These differences are sufficient to generate changes in most of the 
proteins: indeed, 83 percent of the 231 coding sequences, including 
functionally important genes, show differences at the amino-acid sequence 
level," they added.

"Our data suggest that indels within coding regions (genes) represent one 
of the major mechanisms generating protein diversity and shaping higher 
primate species."

In other words, while the genes and other DNA may look the same in 
chimpanzees and humans, the proteins they eventually code for can be very 
different.

This supports what genetic researchers have been saying lately -- that 
subtle changes in the genetic code that reach far beyond the genes 
themselves may be extremely important to biology.

While there may be no more than about 30,000 to 40,000 human genes, there 
are more than 250,000 different proteins.

The researchers tried to calculate what the genetic code of the original 
ancestor of both looked like, 6 million to 7 million years ago.

It looked to them as if the original ancestor of human chimps had a larger 
genome, and each species pared it down differently as they evolved.

Some of the genetic differences they found may have direct implications for 
disease. They found differences between chimp and human immune system 
genes, for instance, and molecules involved in early brain development.

 -- 
Eric Brager           ^ 
eric AT brager.com      /e\
eric AT looney.com      ---