Size doesn't matter

As scientists unveil the human genome findings, it turns out we have a lot fewer genes than we'd thought, and not many more than a fruit fly.

By Arthur Allen

Feb 13, 2001 | If fate is truly written in our genes, it must be some cosmic scriptwriter's idea of a joke. Because our genetic code is awfully similar to that of the fruit fly.

In a Washington hotel room jammed with Nobel laureates and other brainiacs, two competing groups of researchers presented the 3 billion letters of the human genome to the public Monday with a whimper of surprise. Human genes, it turns out, are remarkably similar to those of lower life forms. Whatever it is that makes us unique is probably not solely in the code that DNA uses to instruct our cells to make proteins.

The biggest surprise of the rough analysis of the first sequencing of the human genome was the number of genes it contains. For years scientists had been predicting that human DNA would contain somewhere between 100,000 and 140,000 genes. It turns out we may have as few as 26,000 -- a genome about the size of a corn plant, with roughly a third more genes than the fruit fly.

When it comes to numbers of genes, size definitely does not matter. Not only that, but our genes look pretty similar, in structure, to most of the genes in fruit flies, roundworms and even brewer's yeast.

For example, we seem to have only about 300 genes that mice lack. We also have about 200 genes that have come down to us from bacteria. Some of those genes have important functions in the brain -- one, for example, is key to the processing of certain antidepressant drugs.

It turns out only 1 percent of our DNA is what we think of as genes -- i.e., chemical components that help build proteins, the building blocks of our bodies; scientists had thought at least 3 percent of our DNA was coded for proteins. Half of the rest of our DNA is made up of "jumping genes," semidecrepit strings of DNA that migrate like viruses in and out of our genomes with mysterious purpose.

People used to call jumping genes and other noncoding segments "junk DNA." Nobody was calling it junk on Monday. "Probably these other regions of DNA are important," said MIT's Eric Lander, a leader of the decoding effort. But neither he nor anyone else was all that sure how.

If nothing else, Monday's news will necessitate an overhaul of the bromides commonly used to describe our relationship with our DNA. We should no longer be identifying ourselves by "what's in our genes." It's not that we aren't biological beings. But our I.Q. and hair color and foot tapping and propensity for diabetes, and all the rest, are clearly caused by a mishmash of things -- not just genes and environment, but also interactions among genes and proteins and all the noncoding DNA, whose functions are still shrouded in a good deal of mystery.

There was something breathtaking about this event. Maybe it was the fact that all these intensely intelligent people, with the most modern machines at their disposal, had been taken by surprise by what they diligently found. In a way, it was science at its best.

As an enormous 15-foot banner filled with tiny script was trotted out before the podium -- a graphic representation of the DNA sequence and genes on a single chromosome -- the scientists expressed amazement at what they'd accomplished.

"We felt like Lewis and Clark, crossing new mountain ranges and entering new valleys, seeing new rivers," said Robert Waterston, who headed one of the large sequencing labs, at Washington University in St. Louis. "Even two years ago I didn't know if I'd live to see this day."

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