Deoxyribonucleic Acid - the fingerprint of life also know as DNA was first mapped out in the early 1950's by British biophysicist, Francis Harry Compton Crick and American biochemist James Dewey Watson. They determined the three-dimensional structure of DNA, the substance that passes on the genetic characteristics from one generation to the next. DNA is found in the chromosomes in the nucleus of a cell.
"Every family line has it's own unique pattern of restriction-enzyme DNA fragments. This variation in patterns of DNA fragments found in human genetic lineages is called restriction-fragment length polymorphism'(RFLP)." (Louis Levine, ?) Because each person, except for identical twins(which have the exact same DNA), is formed from two family lines the pattern of sizes of the fragments from an individual is unique and can serve as a DNA fingerprint of that person. These fingerprints' have became very important in identifying criminals in a number of violent crimes where the victims aren't able to. Blood or semen stains on clothing, sperm cells found in a vaginal swab taken after a rape, or root hairs are all available for analysis. Although other body tissues such as skin cells and saliva can provide genetic information about a person for Forensic Science purposes, blood is the most useful source of inherited traits. If the DNA fingerprints produced from two different samples match, the two samples probably came from the same person.
Here are some examples of court cases where DNA plays an important roll in the outcome of the trial.
Hauppauge N.Y.: After 11 years in prison for rape Kerry Kotler cried tears of joy becoming one of the first convicts in the United States to be freed by DNA technology. At a banquet held for Kotler he received a standing ovation from the guest's of his lawyer, Barry Schech and Peter Neufeld, who would later use their DNA expertise to help free O.J. Simpson.
Now the very weapon used to free Kotler will be used against him and instead of his lawyers praising DNA testing they will be trying to tear it down. Four years after being released from prison Kotler was charged with another rape and the DNA test matched him to the semen found on the victims clothing. Posing as a police officer he forced a 20 year old college student off the highway and raped her. A partial license plate number and a description of the car led them to Kotler. The semen matched Kotler's blood and the chances of the semen being somebody else's is one to 7.5 million. Also, dog hairs on the victims clothing matched hairs from Kotler's German shepherd. Kotler, 37, is free on $25000 bail and could get up to 50 years in jail if convicted of rape and kidnapping. Anamosa, Iowa: 22 year old Cathy Jo Bohlken was sexually assaulted and murdered. Genetic evidence from fluid taken from her body points to an 18 year old named Travis Jamieson. Bohlkan's body was found DEC 26, 1993 on the floor of her duplex with a bag over her head and her hands wrapped with duct tape. Autopsy shows she died of multiple stab wounds. The search of a pick-up truck registered to Jamieson's parents revealed a utility knife and a "red-brown stain" on the steering wheel. (http://www.wcinet.com/th/news/th0208/stories/1355.htm) Norman, Okl:Thomas Webb III was released after more than 13 years in prison for a 1982 rape. DNA testing was not available at the time so Gale Webb, Thomas' wife, pushed authorities to use DNA genetic profiling on the 14 year old evidence. These DNA tests ruled him out as a suspect.
Santa Ana, Calif: Kevin Lee Green cried as the judge apologized for the mistake and freed him from prison after nearly 17 years. He was convicted of killing his unborn baby and nearly beating his wife to death.
He was released as authorities prepared to charge a convicted rapist with the murder of Green's unborn child. The reversal of Green's conviction came after another man confessed and his statement was backed up by DNA technology not available in 1980. He was sent to prison on the testimony of his wife who at first didn't remember the attack but that her memory suddenly returned as she read a baby magazine. She testified that her husband severely beat her because she refused sex. Green insisted that he left to get a cheeseburger and came home to see a man leaving in a van. Authorities now believe the attacker was Gerald Parker, 41, who owned a van at the time. He is suspected to be in the "bedroom basher" serial killings in Orange County in 1978 and 1979. (http://www.wcinet.com/th/news/th0622/stories/15897.htm) San Francisco:Theodore Kaczynski, 54, has been jailed in Helena, Mont. since his arrest April 3rd at the mountain cabin where he spent most of his time since quitting his job at the University of California in 1969. The former math professor has been charged with possession of bomb-making material. Kaczynski, the suspected Unabomber is blamed for 3 deaths and 23 injuries in an 18 year bombing spree that begun in 1978. DNA tests of saliva found on two letters-one sent by the Unabomber and one by Kaczynski to his family-showed a genetic link. An FBI investigation found common phrases and misspellings between his writings and documents say were written by the Unabomber. A search of his cabin revealed the original copy of the Unabomber's 35000 word anti-technology manifesto, a typewriter used on the manifesto, bombs, bomb parts and detonators. (http://www.wcinet.com/th/news/th0615/stories/14962.htm)
The accuracy of DNA fingerprinting has been challenged for many reasons. One reason is because DNA segments rather than complete DNA strands are fingerprinted, a DNA fingerprint may not be unique. There have been no large scale research to confirm the uniqueness of DNA fingerprints. Also, DNA fingerprinting is often done in private laboratories that may not follow uniform testing standards and quality controls, and since humans must interpret the test, human error could lead to false results. DNA fingerprinting is expensive, so suspects who are unable to provide their own DNA experts may not be able to adequately defend themselves against charges based on DNA evidence.
There are two methods which can be used to test DNA. "The older one called restriction-fragment length polymorphism' (RFLP) takes up to two weeks to complete and requires a larger supply of high quality, uncontaminated DNA. The good thing about this test is that it finds the random repeats'. These extra chemical units give everyone's DNA a unique pattern. The newer method is called Polymerase Chain Reaction (PCR). This system uses an enzyme that can be directed towards regions of DNA known to contain variations. The results can be printed out in a series of blue dots. The good thing about this method is that it can be completed in a few days and it only requires a small amount of DNA, even if it has begun to degrade and deteriorate. Although PCR is faster and easier it does have its drawbacks. The old method finds rarely repeated characteristics while PCR finds genetic features shared by many people. That means that the older method might show one person in a billion is likely to have the same DNA as a suspect while PCR shows that the same characteristics may be shared by as many as one in a thousand.(Nichols, P58)
The discovery of DNA has led to tremendous advances in solving crimes but there is still a lot to learn. The technology of DNA is still in it's infancy and as it develops and as lab procedures become standardized DNA will be an even more powerful force in the courtroom.