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Last Updated: Monday, 5 April 2004, 10:59 GMT 11:59 UK
New light shed on chimp genome
By Becky McCall

Chimps, BBC
The interest is in where our codes have gone separate ways
A comparison of the chimp and human genomes casts new light on why the two species are so different despite having very similar genetic code.

Scientists have long speculated over what makes humans so different from their closest relatives, the apes.

One of the leading scientists on the project says the answer lies in the process that orchestrates the genes as the chimpanzee is developing.

The human and chimpanzee genomes differ by just 1.2% between the coding genes.

Professor Svante Paabo, from the Max Planck Institute, Leipzig, Germany, is investigating which genes are present and the manner in which they are expressed.

The double-stranded DNA molecule is held together by chemical components called bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
Groupings of these letters form the "code of life"; there are estimated to be about 3.1bn base pairs in the chimp genome wound into 25 distinct bundles, or chromosomes
Written in the DNA are possibly 25-30,000 genes which chimp cells use as templates to make proteins; these sophisticated molecules build and maintain the animal's body
Brain scan

In particular, he believes the key lies in the degree to which they are expressed in each species.

"It's about the extent to which genes are turned on, where and when in the brain.

"What we have now done is systematically looked at gene activity in the brain of chimpanzees, humans, orang-utans and macaques and when we compare them the surprising finding is that we actually find quite a lot of differences.

"And in any particular part of the brain about 10% of our gene activity differs from those of chimpanzees," said Dr Paabo.

The key to the distinction between the two species could lie in the functional importance of different levels of gene expression.

By mathematically modelling the changes seen in gene expression between the two species, Paabo hopes to identify those genes which could have been acted on by natural selection more strongly than others.

Paabo, MPG
In any particular part of the brain about 10% of our gene activity differs from those of chimpanzees
Prof Svante Paabo
There are also small but important differences between the individual genes. So far Dr Paabo has found two tiny but important differences in the gene FoxP2, thought to be responsible for speech and language skills.

Chimps are much better at sniffing things out than we are, so unsurprisingly there are differences in genes associated with smell.

"The gene involved in our sense of smell encodes for receptors in our noses, and we have found that we are losing a large fraction them and are becoming progressively worse at smelling," Professor Paabo said.

"So as our language ability has improved, our sense of smell has deteriorated. The other gene is that which has been positively selected for speech and language ability within the last 200,000 years or so,"

There are likely to be many more subtle differences as groups across the world begin direct comparisons.

In particular the Human Genetics group at the Sanger Institute in Cambridge is intrigued by why chimps are immune to many human diseases, such as malaria and Aids. According to Dr Tim Hubbard:

"By looking closely at the variation of disease genes between Chimps and humans we'll gain a greater understanding of disease processes which in turn may lead to the development of better medicines."

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17 Apr 02 |  Science/Nature
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07 Jan 08 |  Science/Nature
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22 Aug 00 |  Science/Nature

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