STATE OF THE ART
People have been genetically modifying plants and livestock for centuries through selective breeding, but the deciphering of DNA's structure opened the door to much more radical manipulation. Among the first modified crops to hit the markets was the Flavr Savr tomato, genetically tweaked to stay ripe longer. Introduced in 1994, it failed to catch on with consumers because of its bland taste.
Farmers embraced genetically modified crops, though, and they now grow more than three dozen types to save on production and labor costs. The most popular corn, cotton and soybeans have been altered to resist insects or weed-killing chemicals that are sprayed on fields. Two-thirds of the soybeans planted in the United States two years ago were resistant to herbicides, about triple the amount of four years earlier. Scientists also have engineered "yellow rice," a strain rich in vitamin A, to battle malnutrition in developing countries.
In 1996, scientists in Scotland cloned a sheep named Dolly from a cell taken from an adult sheep. The development created a sensation, and opened the possibility of using genetic manipulation to produce entire flocks of prize-winning livestock from a single animal. Many consumers, however, remain leery of "Frankenfoods." Concerns have been raised about the potential for genetically modified crops to harm butterflies, wild plants and even humans. Though research has found no health risks, European countries insist on labeling genetically modified foods, and some developing countries have balked at accepting relief shipments of modified grain from the United States.
Besides producing stronger, more healthful foods, biotechnology has brought breakthroughs in producing drugs, screening for diseases and cleaning up environmental contamination.
Dozens of bioengineered drugs have been approved for various medical conditions; synthetic insulin is used by millions for treating diabetes. DNA manipulation also has yielded new diagnostic tests for AIDS, hepatitis and other infectious diseases.
By mixing and matching the DNA of different bacteria, scientists have created new microorganisms that can clean up oil spills or toxic-waste dumps by "feeding" on the chemicals.
From the crime scene to the courthouse, the use of DNA as proof of identity has changed how crimes are investigated and solved, how victims of mass disasters are recognized, and how paternity disputes are settled.
Developed in 1985 by British geneticist Alec Jeff-reys, the technique is based on the concept that each person's DNA contains unique patterns and that these patterns can be used like a biological Social Security number or bar code.
Although a few scientists still debate the reliability of DNA fingerprinting, most judges and coroners accept its conclusions. From the crash of the space shuttle Columbia to the attack on the World Trade Center, it has proven indispensable in identifying the remains of disaster victims.
As researchers sort through the genetic instructions encoded on DNA, they have linked about 2,800 medical disorders with particular defects in individual genes including fatal diseases such as cystic fibrosis. They also have identified genetic glitches that make people prone to more common illnesses such as heart disease, breast and colon cancer, diabetes and arthritis, though the causes cannot be traced to specific genes.
Although scientists have successfully corrected or replaced defective genes in laboratory animals, efforts to try gene therapy in humans have been problematic, marked by the death in 1999 of an 18-year-old participant in a gene therapy trial at the University of Pennsylvania. Human trials of a promising treatment for "bubble boy" disease a rare disorder in which children are unable to develop immunity against illness were halted this year after two test subjects developed leukemia. Doctors in Philadel-phia recently won government approval, though, to try a new treatment for Parkinson's disease that involves injecting a gene into a person's brain.
ON THE HORIZON
Will DNA someday be used to break encrypted messages for the military or scour genetic databases for signs of disease the kind of jobs performed by electronic computers today? That's what the scientists working in the hot field of DNA computing think.
Think of DNA as nature's version of a supercomputer. The molecule can store huge amounts of information indeed, the recipe for an entire person and is capable of performing millions of calculations at once.
While electronic computers use a binary system of ones and zeroes, DNA computers hinge on the molecule's four chemical bases and their ability to pair naturally with one another.
Since the mid-1990s, researchers have found problems suited to DNA's quirky calculation method trivial puzzles in math, logic, even chess. But as scientists learn to more adeptly manipulate the molecule, they speculate that even more applications will emerge, although it is doubtful that DNA computers will ever be doing your taxes.
DNA is an important, if limited, crime-fighting tool capable of identifying a suspect by matching one genetic sample to another. But what if it could tell police that their suspect was a white male with red hair, blue eyes and a cleft chin?
It is not yet possible to generate a sketch from a scrap of DNA. But by comparing the DNA of hundreds of people, scientists have found patterns that are leading to genetic tests for hair color, eye color and even ethnicity. Other researchers, meanwhile, are working to find markers for bone structure.
The tests are bound to be controversial. Civil libertarians worry that the technique will lead to gross invasions of privacy. Some scientists argue that the strategy is a dead end, that it's impossible to divine a person's appearance from DNA. But British police have solved crimes with the technique and think it may become the ultimate eyewitness.
Scientists announced last year that they had created the polio virus by stitching together snippets of DNA obtained through a mail-order supply company.
Experts wonder whether the capability of creating new life forms is not far behind. Millionaire molecular biologist Craig Venter has embarked on an effort to build a bug from scratch using Mycoplasma genitalium, a bacterium that lives in human genital tracts, as a starting point.
Scientists are debating the usefulness of custom-made microbes. Some worry that terrorists could unleash unstoppable killer bugs. But Venter and others argue that the science will result in microbes that suck greenhouse gasses from the atmosphere, excrete hydrogen fuel or destroy toxic waste.
Doctors helping parents conceive a child through in-vitro fertilization are screening embryos for genetic defects, and some fertility clinics offer prospective parents the opportunity to choose the sex of their baby before the fertilized embryo is implanted in the mother's womb. A Colorado couple recently gave birth to a son chosen through genetic screening so he could provide bone marrow to his older sister, who has a rare genetic disease. Some think, or worry, that engineering the DNA of offspring for desirable traits is only a short step further. Nobel laureate James D. Watson, whose co-discovery of DNA's structure launched the genetics revolution, has asked: "If we could make better human beings by knowing how to add genes, why shouldn't we?"