How "DNA" testing works

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The tools for solving rapes and murders have improved rapidly. Five years ago DNA tests couldnt link suspects to hair or semen found on a victim. Today a crime lab can identify unique DNA patterns in a tiny sample of just 100 to 200 cells. The steps scientists take to implicate or exonerate suspects:


  1. Collect biological materials from the crime scene and the suspect under investigation, such as blood, hair, semen or saliva. Every cell is a unique library of DNA sequences. The goal is to find out if the forensic and suspects samples match.
  2. Isolate pure DNA by mixing the sample with chemicals that break down other cellular material. DNA molecules consists of paired filaments that interlock like zippers, and each filament is made up of chemicals “bases” (A, C, T and G) aligned in unique sequences.
  3. Amplify the DNA by separating paired filaments and mixing them with short fragments known as primers. When a primer locks onto a particular site on a sample DNA molecule, it triggers production of a longer fragment that matches a piece of the sample.
  4. Segregate the resulting DNA strands. A sample mixed with 13 primers multiplies into millions of distinctive molecules. Exposed to an electrical current, the molecules a sorted into color-coded bands on a gel.
  5. Compare the crimescene samples with the suspects. Scientists say its virtually impossible for unrelated people to match up perfectly on 13 different levels. If samples do, odds that theyre from one person are overwhelming.


Helped prove the innocence of Anthony Porter, who at one point had been just two days shy of lethal injection for a pair of 1982 murders. Once again, the issue in Illinois wasn't the morality of death sentences, but the dangerously sloppy way in which they were handed out. Once again a confession from another man helped erase doubt that the man convicted of the crime, who has an IQ of 51, had committed it.

By last fall the list of men freed from death row in Illinois had grown to 11. That's when the Chicago Tribune published a lavishly researched series explaining why so many capital cases were suspect. The Tribunes digging found that almost half of the 285 death-penalty convictions in Illinois involved one of four shaky components: defense attorneys who were later suspended or

disbarred, jailhouse snitches eager to shorten their own sentences, questionable "hair analysis" evidence or black defendants convicted by all-white juries. What's more, in the weeks after those stories appeared, two more men were freed from death row. That pushed the total to 13 - one more than the number of inmates Illinois had executed since reinstating the death penalty in 1977.

The Porter case and the Tribune series were enough for Governor Ryan. On Jan. 31, he declared a moratorium on Illinois executions, and appointed a commission to see whether the legal process for handling capital cases in Illinois can be fixed. Unless he gets a guarantee that the system can be made perfect, Ryan told NEWSWEEK last week, "there probably won't be any more deaths," at least while he's governor. "I believe there are cases where the death penalty is appropriate," Ryan said. "But we've got to make sure we have the right person. Every governor who holds this power has same fear I do.”

But few are acting on it. In the wake of the Illinois decision, only Nebraska, Maryland, Oregon and Nrw Hampshire are reviewing their systems. The governors of the other states that allow the death penalty apparently think it works adequately. If they want to revisit the issue, they might consider the following factors:

Race: The role of race and the death penalty is often misunderstood. On one level there's the charge of institutional racism: 98 percent of prosecutors are white, and, according to the NAAGP, Legal Defense Fund they are much more likely to ask for the death penalty for a black-on-white crime than when blacks are the victims. Blacks convicted of major violent offenses are more likely than white convicts to end up on death row. But once they get there, blacks are less likely than white death-row inmates to he executed because authorities are on the defensive about seeming to target African-Americans. The result is both discrimination and reverse discrimination - with deadly consequences.

The risk of errors: The more people on death row, the greater chance of mistakes. There are common elements to cases where terrible errors have been made: when police and prosecutors are pressured by the community to "solve" a notorious murder; when there's no DNA evidence or reliable eyewitnesses; wnen the crime is especially heinous and draws large amounts of pretrial publicity; when defense attorneys have limited resources, if authorities were particularly vigilant when these issues were at play, they might identify problematic cases earlier.

Deterrence: Often the first argument of death-penalty supporters. But studies of the subject are all over the lot, with no evidence ever established of a deterrent effect. When parole was more common, die argument earned more logic. But nowadays first-degree murderers can look forward to life without parole if caught, which should in theory deter diem as much as die dead penalty. It's hard to imagine a criminals thinking: "Well, since Г might get the death penalty for this crime, 1 won't do it. But if it was only life in prison, I'd go ahead."

inadequate counsel: Beyond the incompetent lawyers who populate any court-appointed system, Congress and the Clinton administration have put the nation's 3,600 death-row inmates in an agonizing Catch-22. According to the American Bar Association Death Penalty Representation Project, in a state like California, about one third of death-row inmates must wait for years to be assigned lawyers to handle their state direct appeals. And at the postconviction level in some suites, inmates don't have access to lawyers at all. The catch isdiatdie 1996 And -Terrorism and Effective Deatii Penalty Act has a statute of limitations requiring diat inmates file federal habeas corpus petitions (requests for federal court review) within one year after die end of their direct state appeal. In other words, because they have no lawyer after their direct appeals, inmates often helplessly watch die clock run out on their chance for federal review. This cuts down on frivolous appealsbut also on ones that could reveal gross injustice.

Fact-finding: Most states aren't as lucky as Illinois. They don't have reporters and investigators digging into die details of old cases. As die deadi penalty becomes routine and less newsworthy, the odds against real investigation grow even worse. Аж1 even when fresh evidence does surface, most states place high barriers against its use after a trial. This has been standard in the legal system for generations, but it makes little sense when an inmate's life is at stake.

Standards of guilt: In most jurisdictions, die judge instructs the jury to look for "guilt beyond a reasonable doubt." But is that the right standard for capital cases? Maybe a second staridard like "residual doubt" would help, whereby if any juror harbors any doubt whatsoever, the conviction would stand but the death penalty would be ruled out. The same double threshold . might apply to cases involving single eyewitnesses and key testimony by jailhouse snitches with in-----

Cost: IJnless executions are dramatically speeded up (unlikely after so many mistakes), the death penalty will remain far more expensive than life widiout parole. The difference is in the upfront prosecution costs, which are at least four times greater dian in cases where death is not sought. California spends an extra $90 million on its capital cases beyond die normal costs of the system. Even subtracting pro bono defense, the system is no bargain for taxpayers.

Whether you're for or against die deadi penalty, it's hard to argue diat it doesn't need a fresh look. From America's earliest days, when Benjamin Franklin helped develop the notion of degrees of culpability for murder, diis country has been willing to reassess its assumptions about justice. If we're going to keep die deadi penalty, die public seems to be saying, let's be damn sure we're doing it right. DNA testing will help. So will odier fixes. But if, over time, we can't do it right, then we must ask ourselves if it's worth doing at all.







The opening DNA is a new era in development of a science and society, it opens new opportunities, which were inaccessible earlier, and is capable to help not only scientist and patient, but also policeman with disclosing a crime. Now already it is impossible to present as five years ago managed without any help of DNA.

Now the laboratory can identify samples found on a place of a crime, with samples suspected, and then to make a conclusion about participation suspected with accuracy on 99 %.

The analysis DNA consists of five stages:





5)Compare , during which is found out, whether the found samples on a place of a crime suspected belong. It is very heavy process, which requires large material inputs, and human forces. But result cant be valuable.

As the opening DNA has helped sharply to lower a judicia