Ceilidh

Michael Zey
futurist3000@aol.com

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 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.

"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 proteins.

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

It appeared to them that the ancestor had a larger genome, and each species pared it down differently as it 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.