New Map of the Human Genome

A team of Ohio State University genetics researchers has produced a third map of the human genome, this one containing twice the number of genes proposed by two maps announced with great fanfare earlier this year.

In February, teams of researchers from Celera Genomics, a private biotechnology firm, and the Human Genome Project, the federally funded effort to map the genome, simultaneously published their findings in the journals Science and Nature, respectively. Both of these reports proposed that the human genome consists of some 35,000 genes, far less than the estimate of 100,000 to 120,000 genes that researchers had long predicted.

By contrast, the new Ohio State gene map, published in the journal Genome Biology, identified between 65,000 and 75,000 potential genes.

"We ended up with a higher estimated number of genes than the other two teams because we compared 13 different gene databases to the DNA sequences in the draft genome produced by the Human Genome Project," said Bo Yuan, head of Ohio State's Division of Human Cancer Genetics bioinformatics group.

The genome map in Science and, particularly, the map in Nature, relied mainly on only two databases to identify genes on their respective genome maps, Yuan said.

"We used more experimental evidence in assembling our map, and that suggests that there are probably between 65,000 and 75,000 transcriptional units," said Yuan. A "transcriptional unit" is a length of DNA that shows strong evidence of being a gene but which still requires future verification.

"Some researchers are unsettled by the certainty with which the Human Genome Consortium is presenting its lower gene count," said Fred Wright, assistant professor of human cancer genetics and lead author of the paper. "In my view, the final number of genes-when it is known-will lie somewhere between their high of 40,000 and our value of 70,000."

"The computations involved millions of DNA sequences and were extremely time-consuming," added Wright. "One of the databases had over 2 million sequences, each of which had to be searched against the entire 2.8 billion base pairs in the genome draft. "Figuring out where those 2 million sequences belonged was, by itself, a major computational task."

SOURCES:
Genome Biology, July 2001; 2(7):0025.1-0025.18
Ohio State University (http://www.osu.edu)

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