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Fewer Genes in “Finished” Human Genome Sequence

By Edward R. Winstead

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Human Genome

The estimated number of human genes has dropped below 25,000, according to a new analysis of the “finished” human genome sequence. This is a third fewer genes than was reported three years ago by the consortium known as the Human Genome Project and the company Celera Genomics, which published independent drafts of the human genome sequence.

Since then, members of the consortium have improved the accuracy of their draft. Most of the 150,000 gaps in the draft sequence were filled in, leaving 341 gaps today. And as happens in genome projects, the consortium discovered that many DNA sequences originally thought to be genes are not really genes after all but rather so-called pseudogenes.

“The number of genes went down mostly because we’re getting better at distinguishing between genes and pseudogenes in the sequence,” says Adam Felsenfeld, who directs the Large-Scale Sequencing program at the National Human Genome Research Institute in Rockville, Maryland.

The new estimate of 20,000-25,000 human genes is reported in Nature as the consortium marks the end of the finishing phase of the project. This phase cost about $320 million, or roughly the same amount of money spent to generate the original draft.

Some people may be confused by the news that the human genome has been sequenced. After all, we have heard this news twice before, first at a White House ceremony in February 2001, when the drafts were completed, and again in April 2003, when the consortium announced “the successful completion of the Human Genome Project.”

And that’s not likely to be the end of the story. There are some regions of the human genome that cannot be sequenced using current methods, so it’s likely that five years from now there may be news stories about the completion of the human genome.

International Human Genome Sequencing Consortium. Finishing the euchromatic sequence of the human genome. Nature 431, 931-945 (October 21, 2004).

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