Genetically speaking, chimps and humans differ more than expected, say a team of researchers who have just completed the first detailed analysis of a chimp chromosome. The new study of chimp chromosome 22, published in Nature, reveals surprising differences between human genes and those of our closest animal relative.
Scientists published a rough draft of the entire chimp genome in December 2003, and estimated that around 99.2 per cent of it is identical to our own genetic code. However, researchers need a 'finished' DNA sequence, which has been proof-read several times, before they can make detailed comparisons with other species. Otherwise, errors in the draft version could show up as genuine DNA differences. So a team of scientists from Asia and Europe compared a complete version of chimp chromosome 22 with its human counterpart, chromosome 21.
The researchers found that 1.44 per cent of the DNA 'letters' that make up the two chromosomes differs between the two species. They also identified 698,000 sections of DNA that have either been inserted or deleted from one genome or the other. But surprisingly, many of these differences were in DNA that makes up genes, rather than the large tracts of 'non-coding' DNA that does not form genes. The results showed that 83 per cent of the 231 genes compared had differences that affected the protein they make. And 20 per cent of the differences caused 'significant structural changes' to the corresponding protein, which could alter their role in the body.
A final version of the entire chimp genome is due to be published this summer. Scientists are hoping that a detailed comparison of chimp DNA with our own will reveal the key differences that make us human. But it now seems that identifying the genes behind uniquely human traits, including susceptibility to some diseases, will prove more complicated than first thought.
Also published in Nature last week were the final versions of human chromosomes nine and ten. An international consortium unveiled the final version of the entire human genome on 14 April 2003. Researchers have since been looking at each of its 24 different chromosomes in detail, to identify the coding stretches of DNA that make up genes. They have also been filling gaps - stretches of DNA sequence that could not easily be determined - and double-checking for any errors. As well as chromosomes nine and ten, scientists have also published complete, fully-analysed sequences for chromosomes 19, 13, 22, 21, 20, 14, 7, 6 and the Y chromosome
Sources and References
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Chimp chromosome creates puzzles
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Chimps are not like humans
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Surprises in first map of chimp chromosome
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Researchers complete analysis of human chromosomes nine and 10
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