Newspaper article International New York Times

The Continuing Evolution of DNA ; Some Human Genes Take on Essential Tasks, and Others Fall to Wayside

Newspaper article International New York Times

The Continuing Evolution of DNA ; Some Human Genes Take on Essential Tasks, and Others Fall to Wayside

Article excerpt

Studies show that some human genes take on essential tasks, and others fall to the wayside.

Each of us carries just over 20,000 genes that encode everything from the keratin in our hair to the muscle fibers in our toes. It's no great mystery where our own genes came from: Our parents bequeathed them to us. And our parents, in turn, got their genes from their parents.

But where along that genealogical line did each of those 20,000 protein-coding genes get its start?

That question has hung over the science of genetics since its dawn a century ago. "It's a basic question of life: How evolution generates novelty," said Diethard Tautz of the Max Planck Institute for Evolutionary Biology in Plon, Germany.

New studies are now bringing the answer into focus. Some of our genes are immensely old, perhaps dating all the way back to the earliest chapters of life on Earth. But a surprising number emerged more recently -- many in just the past few million years. The youngest evolved after our own species broke off from our cousins, the apes.

Scientists are finding that new genes come into being at an unexpectedly fast clip. And once they evolve, they can quickly take on essential functions. Investigating how new genes become so important may help scientists understand the role they may play in diseases like cancer.

"It's premature to make any grandiose claims, but there's a coherence that's emerging," said David Begun, an evolution scientist at the University of California in Davis.

Geneticists first speculated about the origin of genes in the early 20th century. Some proposed that when cells duplicate their DNA, they accidentally copy some genes twice. At first the two genes are identical. But later, they evolve into different sequences.

At the end of the century, as scientists gained the ability to read the precise sequence of DNA, they found that this hunch was correct. "It became clear that gene duplication played a role in evolution," Dr. Tautz said.

As genes duplicate over millions of years, they can grow into so- called gene families, each containing hundreds of similar genes.

One family, for example, is essential for our sense of smell. These genes encode 390 different kinds of proteins produced in our noses, called olfactory receptors. Each olfactory receptor has a slightly different structure, allowing it to capture a different set of molecules.

Over long periods of evolutionary time, some copied genes change drastically -- so drastically, in fact, that they take on entirely new tasks.

Consider hemoglobin, which stores oxygen in red blood cells for delivery throughout the body. Scientists have found that it belongs to a family of genes that do many different things with oxygen and recent studies suggest that it evolved from proteins that grabbed extra oxygen molecules inside cells before they could do harm.

The case for gene duplications became so strong that many scientists grew convinced that it was the source of all new genes. They speculated that when life originally emerged billions of years ago, the first primordial microbes had a tiny set of genes. Those genes then duplicated over and over again to give rise to all the genes on Earth today. …

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