SHANGHAI, May 27 (Xinhuanet) -- There are more differences between a chimpanzee and a human being than once believed, according to a new genetic study.

    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 crucial.

    "Clearly, the genomic differences between humans and chimps aremuch more complicated than conventional wisdom has portrayed," says a report by an international research team, published in this week's issue of the journal Nature.

    The team of scientists from China, Japan, Germany and the Republic of Korea (ROK) compared chromosome 22 on three different chimpanzees to its counterpart in humans, chromosome 21, where certain genetic problems can lead to severe diseases, including Down's syndrome.

    Insiders say 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.

    Experts from the South Research Center of China's International Human Genome Program are heavily involved in the research program,decoding and sequencing more than 5 million, or 16 percent, of thetotal 33 million genes over the past three years.

    The scientists looked for differences that would help separate the human sequence from the chimp sequence, and found 1.44 percent of the DNA was different, higher than the 1.23 percent reported inJanuary 2002.

    They reported in Nature that many of the differences were within genes, the regions of DNA that code for proteins: 83 percent of the 231 genes compared had differences that affected the amino acid sequence of the protein they encoded, and 47 showed "significant structural changes".

    In addition, there were nearly 68,000 regions that were either extra or missing between the two sequences, which made the human chromosome 21 longer than the chimpanzee chromosome 22 and may help scientists study further into advanced patterns of neural activities, such as cognition and thinking.

    According to the report, chromosome 22 makes up only one percent of the genome, so in total there could be thousands of genes that significantly differ between humans and chimps, which could make it much harder to find the key changes that turned apes human.

    The researchers tried to calculate what the genetic code of the original ancestor of both looked like, 6 million to 7 million years ago. The original ancestor of human chimps, they said, probably 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 inearly brain development.

    Besides, significant genetic differences in the brains and livers of the two species, for example, may help explain why chimps rarely have symptoms of complicated human diseases, such as AIDS, malaria and hepatitis C, even after they are infected with the same viruses. Enditem