回答{TSE}题： DNA testing DNA testing reveals the genes of each individual person. Since the early twentieth century scientists have known that all human characteristics are contained in a person's genes and are passed from parents to children. Genes work as a chemical instruction manual for each part and each function of the body. Their basic chemical element is called DNA, a copy of which can be found in every cell. The existence of genes and the chemical structure of DNA were understood by the mid-1900s, but scientists have only recently been able to identify a person from just a drop of blood or a single hair.One of the most important uses of DNA testing is in criminal investigation. The very first use of DNA testing in a criminal case was in 1985 in Great Britain, when a man confessed to killing a young woman in the English countryside. Because police had found samples of the killer's DNA at the scene of the crime, a biologist suggested that it might be possible to compare that DNA to some from the confessor's blood. To everyone's surprise, the tests showed that he was not the killer. Nor was he guilty of a similar murder that had happened some time earlier. At that point he admitted that be had confessed to the crimes out of fear and police pressure. The police then asked 5, 000 local men for samples of their blood, and DNA testing revealed that one of them was the real murderer, so the first man was set free. In 1992, two law professors, Peter Neufeld and Barry Scheck, decided to use DNA evidence to help set free such mistakenly convicted prisoners. With the help of their students, they created a not-for-profit organization called the Innocence Project. Most of their clients are poor men, many from racial and ethnic minorities. In fact, studies have shown that U. S. judges and juries are often influenced by racial and ethnic background, and that people from minority groups are more likely to be convicted. Some of these men had been sentenced to death, a form. of punishment used in thirty eight states out of fifty (as of 2006). For most of these prisoners, their only hope was another trial in which DNA testing could be used to prove their innocence. Between 1992 and 2006, the Innocence Project helped free 100 men. Some of these prisoners had been in jail for ten, twenty years or more for crimes they did not commit. However, the goal of the Innocence Project is not simply to set free those who are wrongfully in jail. They also hope to bring about real changes in the criminal justice system. Illinois in the late 1990s, a group of journalism students at Northwestern University were able to bring about such a change in that state. They began investigating some Illinois prisoners who claimed to be innocent. Through DNA testing, the students were able to prove that in fact the prisoners were not guilty of the crimes they had been accused of. Thirteen of these men were set free, and in 2000,Governor Ryan of Illinois decided to stop carrying out death sentences until further study could be made of the prisoners' cases. The use of DNA in criminal cases is still being debated around the world. Some fear that governments will one day keep records of everyone's DNA, which could put limits on the privacy and freedom of citizens. Other people mistrust the science of DNA testing and think that lawyers use it to get their clients free whether or not they are guilty. But for those whose innocence has been proven and who are now free men, DNA testing has meant nothing less than a return to life. And with the careful use of DNA testing, no innocent person should ever be convicted again. {TS}What is the main idea of this passage?