MORE than a dozen police laboratories around the United States use DNA, the genetic code in every human cell, to perform identity tests. This relatively new forensic technique is rapidly gaining in popularity. "The FBI has trained over 240 crime laboratory technicians from 80 different agencies around the country," says John Hicks, assistant director of the Federal Bureau of Investigation Laboratory in Washington, D.C. "Within the next year, I would expect that you would see a tremendous increase in the number of laboratories that are on-line."
The FBI is also laying the groundwork for a national databank of DNA information collected from crime scenes and convicted felons. Such a databank would help in the investigation of crimes and in catching repeat offenders, Mr. Hicks says.
DNA - deoxyribonucleic acid - is the molecular basis for heredity. Scientists say that each individual, except for identical twins, has a unique sequence of DNA.
But DNA identity tests are increasingly coming under attack. Last month in Massachusetts, the state's Supreme Judicial Court ordered a new trial for a man convicted of raping a 14-year-old disabled girl, saying that the scientific community does not have widely accepted uniform methods for testing and interpreting DNA evidence. In Arizona, a superior court judge ruled that the results of a DNA test could not be introduced in a trial because the apparent scientific accuracy of the test might convinc e a jury of the defendant's guilt, even though the scientific community itself has questions about the underlying test.
"They've rushed to the courts with this, instead of doing the real hard groundwork that they need to make a good system," says Richard Lewontin, a professor of population biology at Harvard University, who is an outspoken critic of DNA iden- tification systems.
Proponents of the technology disagree. "Having testified as an expert in over 50 cases, I would say that the introduction and the acceptance of this technology has been very good in the courts," says Michael Baird, director of research at Lifecodes, a New York company that pioneered the identification technique. Dr. Baird says DNA evidence has been used in more than 400 cases.
Using DNA identity testing, sometimes called "DNA fingerprinting," scientists say they can determine if two samples of human tissue or bodily fluids came from the same person. The test needs only tiny amounts of genetic information for success: a drop of blood, saliva, or semen, a few hair roots, or a piece of skin.
THE tests were pioneered between 1982 and 1986 by Cellmark (Rockville, Md.) and Lifecodes (Valhalla, N.Y.). In 1986, the FBI developed its own system, Hicks says.
DNA testing is likely to have the biggest impact in rape cases, says Bruce Budowle, an FBI research chemist. Dr. Budowle notes that "78 percent of rape cases involve semen." With the test and a blood sample from the defendant, law enforcement officials say that they can prove if the semen found with a rape victim came from the suspect.
Indeed, lawyers and prosecutors have latched onto DNA testing as a "magic bullet," says Marjorie M. Shultz, a professor at the University of California's Boalt School of Law. "The hunger for the DNA evidence is the result of our desire to have the perfect truth," she says.
But as with blood types, critics argue, DNA testing can only prove innocence. If two samples of DNA are different, they came from different people. But if two samples are the same, there is always a chance of a random match, because only a tiny fraction of a person's DNA is actually analyzed in the test. Scientists then must use statistics to determine the probability of a chance match, which requires knowing the frequencies of different kinds of DNA in the population being studied.
The problem, Harvard's Dr. Lewontin says, is that geneticists really don't know how many people have the genetic markers used in the tests. "There is a lot of variation from subgroup to subgroup in the American population.... A group of Italian-American extraction might have 200 times the chance of having a particular DNA profile" compared with the rest of the population, he says.
"The FBI doesn't have the databases for the different subgroups. They can't use [the technique] to calculate" the probability of the match, he argues.
FBI scientists disagree. "The population data ... demonstrates that there is very little difference between the Caucasian subgroups and very little difference between the black subgroups," Hicks says. "Between blacks and Caucasians there are some differences, but it is remarkable how small those differences are."
Increasingly, the scientific establishment seems to be accepting the legitimacy of the tests. Last summer, a report issued by the US Congress Office of Technology Assessment (OTA) concluded that "forensic uses of DNA tests are both reliable and valid when properly performed and analyzed by skilled personnel." The report called questions about the validity of the technology or the underlying population genetics "red herrings that do the courts and the public a disservice."
What's needed now, the OTA says, is to make sure that lab technicians are well trained and tests are uniformly interpreted. Nevertheless, concerns remain about what impact genetic testing will have on the courts and on society at large.
A major factor is cost. Although Lifecodes sells a kit that a police laboratory can use to do 50 DNA identification tests for $1,000, the company itself charges $485 to analyze a single sample, Lifecodes' Baird says. The cost of labor and laboratory time accounts for the difference. Test results must be presented in court by experts, adding another $800 to $1,200 per day.
CIVIL libertarians are more worried by the prospect of large-scale DNA testing. "It seems likely that this technology will lead to a national identification system," says Dr. Paul R. Billings, chief of genetic medicine at the Pacific Presbyterian Medical Center in San Francisco.
Today, police forces and legislatures around the country are trying to establish databanks to hold the DNA of people convicted of violent crimes. Such a databank would make it possible to easily identify repeat offenders - especially for crimes like rape. "Women's community groups and sexual assault support groups are very much in favor of this," says Philip L. Bereano, a professor of engineering and public policy at the University of Washington in Seattle. "It has been proposed that since we take the b lood from every newborn, we should just run the DNA test and keep the [record] bars on file."
Already California and Virginia have started taking blood samples from convicts before they are released, Hicks says. And, Dr. Bereano says, "Eleven states have the requirement that DNA typing be done of convicted offenders."
DNA stored in such a databank might be later reanalyzed for other purposes. "Political pressures will grow from the private sector - particularly the insurance industry - to get access to that file," Bereano says.
A person's DNA contains all the individual's genetic information. Future tests might be able to analyze DNA for predisposition to disease or even behavioral characteristics, such as tendency to violence. People whose DNA tested positive might find it impossible to obtain insurance or might be subject to surveillance by the police.
"My own perspective is that it is relatively easy to set up administrative controls to limit the use of and limit access to those kinds of samples," Hicks says. "It would be relatively easy to establish sanctions against those who might abuse the samples."