Chimp DNA yields complex surprises.

Genetic differences between chimpanzees and people are more complicated than scientists had previously suspected, according to an international team.

Asao Fujiyama of the National Institute of Informatics in Tokyo and his colleagues used genetic material from three adult chimps to determine the entire DNA sequence of the animals' chromosome 22. They compared this chimp-chromosome sequence with previously acquired sequence data for its counterpart in people, chromosome 21.

As expected, the sequences, which consist of tens of millions of genetic letters, differ at only about 1.44 percent of those letters, or nucleotides. Surprisingly, though, nearly 68,000 stretches of DNA do differ to some degree between the two species, the researchers report in the May 27 Nature.

Extra sections of about 300 nucleotides showed up primarily in the human chromosome, Fujiyama and his colleagues say. Extra sections of other sizes--some as long as 54,000 nucleotides--appear in both species.

Among the 231 functional genes that could be compared between chimps and people, 47 differed because of DNA insertions or deletions. Preliminary evidence indicates that these modifications frequently alter the types and activities of proteins manufactured by genes.--B.B.