Cracking the Code

Scientists recently mapped you body’s blueprint for life, the human genome. Here’s what that feat means for science and for you.

Where were you June 26? That day marked a milestone in science, one that future historians may compare to the first walk on the moon or even the invention of the wheel. Scientists announced that they had prepared a rough draft of the human genome — the blueprint for human life.

“This is a spectacular achievement,” commented Richard Lifton, head of the genetics department at the Yale University School of Medicine.

Decoding the human genome (JEE-nohm), say scientists, will give them the complete operating instructions for the human body. It will also give them the knowledge that will lead, in time, to reducing or even wiping out thousands of diseases. Finally, it may even give scientists the awesome power to modify the human genome and custom-design human life.

WHAT IS A GENOME?

Decoding the human genome consumed an enormous amount of time (ten years), money ($3.5 billion), and effort. In one lab alone, robots the size of Volkswagen Beetles toiled around the clock, processing snippets of human tissue. Supercomputers in nearby rooms, running on $1 million in electricity each year, analyzed the snippets.

Why was so much work necessary? Because the human genome is the sum of all human deoxyribonucleic (dee-OK-si-righ-boh-noo-KLEE-ik) acid (DNA). DNA is an invisibly tiny substance that stores information in a living thing. In human beings, almost every cell holds an identical copy of DNA.

If you could extract the DNA from one human cell, unravel it, and examine it end-to-end, you’d see a fantastically long chain made up of 3.2 billion microscopic links! Each link is made of one of four kinds of chemicals, or nucleic acid bases: adenine (A), cytosine (C), guanine (G), and thymine (T).

When scientists announced that they had decoded the human genome, they in essence said that they had determined the order in which most of those 3.2 billion bases are linked: TCGGATATTAAG …

ONLY THE BEGINNING

Two teams of scientists broke the code, and they won’t be resting anytime soon. Their work has just begun. As they admitted in June, their work is riddled with errors–inevitable when billions of pieces of data are being handled. In addition, certain sections of the genome have yet to be fully decoded.

Even when scientists completely map the genome, they still must decipher it. And that means isolating its genes. Genes are those parts of the human genome that tell a cell what to do. Genes rule. Every cell type in your body is controlled by a different set of genes.

The human genome is thought to hold about 50,000 genes. So far, only a few of them have been named and fully analyzed.

GENE HUNT

Locating the remaining genes in the human genome will be the next task–and it won’t be an easy one. A gene can be anywhere from 1,000 to 10,000 bases long. To identify which bases make up each gene, scientists will have to sift through long stretches of bases they assume are useless, or “junk DNA.” Scientists estimate that genes make up just 3 percent of the human genome. The other 97 percent is junk DNA.

Even when the genes are separated from the junk, the job will continue. Genes are simply sets of instructions. The actual work in a cell is done by the proteins that the genes instruct the cell to make. Every chemical reaction in the body depends on proteins, of which there are as many as 2 million types. Imagine the job of finding out what all those proteins do! A whole new science of protein research, called proteomics, is just now taking off.

21st-CENTURY DILEMMAS

In the years ahead, genomic knowledge will explode. And with that explosion, scientists expect, will come ways of finding and attacking the faulty genes that cause genetic diseases. (See “Visiting the Gene Doctor,” page 6.) Eventually, brand-new types of genes might be built from scratch–genes that might endow human beings with Hulklike strength or hearts that don’t fail or bodies that don’t grow old.

Such feats will raise profound questions: Who should be permitted to tinker with the human genome? Should parents be allowed to order up genetically programmed children? Should genomic science be used to build a race of superhumans? How could we stop the building of superdestructive humans?

In the meantime, Sydney Brenner, a researcher at the Molecular Science Institute in Berkeley, Calif., estimates that each gene and its products will take a whole lifetime to study. If the human genome holds 50,000 genes, that means 50,000 lifetimes of work, or 50,000 complex, challenging jobs. Many people will one day make their mark in those jobs. Why not you?

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