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Wednesday, 25 September, 2002, 09:30 GMT 10:30 UK
Humans and chimps 'not so close'
Chimpanzee, BBC
The chimp: Still our closest animal relative
Chimpanzees may be the closest relation to humans among animals, but we may not share as much DNA as previously thought.

Most studies suggest that 98.5% of our genetic code can also be found in the chimp.

However, a study published in the journal Proceedings of the National Academy of Sciences says the true difference may be much larger.

In fact, say the researchers, only 95% of our DNA may be the same as the chimpanzee's.

Professor Roy Britten, of the California Institute of Technology, US, said that most studies did not take into account large sections of DNA which are not found on the genome of both man and chimp.

These are "insertions" - where a whole section of genetic code appears in one species but not another, and deletions, in which a chunk is missing.

Professor Britten suspected that these "indels" could be far more significant than the difference revealed by calculating single "base substitutions".

Comparison

He took DNA sequences from the chimp and compared them with the corresponding sections from the human genome.

In these samples, while simply calculating base substitutions revealed a difference of 1.4%, "indels" accounted for a further divergence of 3.9%.

The total difference between humans and chimps in these sequences would therefore be approximately 5.4%.

While it is possible that the chosen sequences - one million bases against a total of three billion - are not accurately representative of the genomes as a whole, Professor Britten believes that 95% sharing would be a "better estimate" overall.

Genome call

The fact that chimps appear resistant to various human diseases such as HIV/Aids and malaria has been used to support calls to work on the complete sequencing of the chimp genome.

This would be a task as demanding as the sequencing of the human genome - which has yet to be completed.

It was claimed that the relatively small difference between human and chimp genomes would offer insights into the gene differences that might render humans more vulnerable to disease.

However, should humans only share 19 out of every 20 base pairs with chimps, as opposed to almost 99 out of every 100, it would make spotting the key genes far more difficult.

See also:

22 Oct 02 | Science/Nature
11 Oct 00 | Science/Nature
22 Aug 00 | Science/Nature
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