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Biology 103
2003 First Paper
On Serendip

Safe, By a Hair

Talia Liben

"A Hair perhaps divides the False and True; and upon what, prithee, may life depend?"

Omar Khayyam

Ron Williamson came within five days of being executed for a crime he didn't commit. He lost twelve years of his life to death row. He is not alone. Chillingly, sixty-eight percent of all death penalty cases are reversed on appeal (Liebman). In the few years since its application in the field of criminal forensics, DNA testing has proven to be the most effective tool ever devised to protect the innocent and convict the guilty.

In 1969, Frederick Miescher identified the substance known as DNA (deoxyribonucleic acid). The components of DNA were rapidly discerned: four nitrogenous bases. Two of the bases, adenine (A), and guanine (G), are purines, and the other two, cytosine (C) and thymine (T), are pyrimidines. In the 1940's, Oswald Avery established that DNA was used to transmit hereditary traits. A decade later, James Watson and Francis Crick famously united to solve the mystery of DNA's shape. They found that A and T can only lie adjacent to each other, C and G can only pair with each other, and together, the separate strands coil into a spiral staircase, called a double helix. The building blocks of life itself had been discovered, but the information remained for many years without any practical application.

Twenty-one year old Debra Sue Carter was brutally raped and murdered in 1982. Jailhouse snitches fingered Ron Williamson, a mentally unstable neighbor of Carter's. A state analyst claimed to link four hairs from the murder scene to Williamson. Williamson's inexperienced court appointed lawyer had never tried a capital case. Despite witnesses who placed Williamson elsewhere, he was found guilty and sentenced to death by lethal injection (Scheck 130-157).

About the time of Carter's murder, geneticist Alec Jeffreys was attempting to identify the segments of genetic material that varied the most from one person to the next, and to discover a method that could make those areas visible. Jeffreys developed a revolutionary technique which we know as "DNA fingerprinting," a laboratory procedure accomplished in six steps: 1) Isolating the DNA from the nucleus by using a detergent to wash away superfluous material. 2) Cutting the DNA into pieces of variable lengths with chemicals called restriction enzymes. The differing lengths of the fragments, due to varying amounts of nucleotides, are called RFLP (restriction fragment length polymorphisms). 3) An agar plate is charged with an electric field. The DNA pieces, having negative charge, drift toward the positive bottom end and separate on the way. 4) The fragments of the DNA spiral staircase are torn apart, separating each purine from its matching pyrimidine. 5) Radioactive markers search out complementary DNA sequences, and attach themselves, marking the spot. 6) The marked DNA is placed next to x-ray film, giving a "signature" unique to that strand of DNA. If two different samples show bands of DNA at the same spot, the geneticist can confirm that the DNA in both lanes is from the same person (Roberts).

Williamson's appellate attorneys sought DNA fingerprinting for the DNA from the murder scene. The DNA from the semen of Debra Carter's rape did not match the DNA from Ron Williamson's blood sample. Not one of the hairs, the most damaging evidence against Williamson, was linked to him by DNA. The test proved, conclusively, that Ron Williamson was not the assailant. Science prevailed over an alleged confession, false witnesses, and ineffective defense counsel. DNA brought him justice.

Fortunately for Williamson, there was sufficient DNA available from the crime scene to conduct the DNA fingerprinting. One significant disadvantage of the RFLP method is that it requires a relatively large amount of DNA. In the messy world of real crime scenes, DNA can be scarce. What was needed was a way to amplify a small sample of DNA. Biochemist Kary Mullis had a breakthrough inspiration that solved this problem. Mullis took a large strand of DNA from which he wanted to isolate a small sequence, and placed it in a test tube along with two small DNA markers. These primers attached themselves to the DNA, delineating the portions of strands Mullis wanted to study. The DNA was only copied between the two markers places on the DNA strand. Mullis then allowed this segment of the DNA molecule to copy itself repeatedly, until he had millions of copies of the sequence (NCBE). Mullis had solved the problem of amplification. As a result, DNA testing can now be performed on specimens that are old, degraded, or of limited quantity.

Interest in DNA testing had been spurred primarily by the desire to find a cure for inherited diseases. Applying the methods to forensics is an innovation that could revolutionize our criminal justice system. Already, national databases are being created which house genetic profiles of convicted felons (Niezgoda). It is possible that newborn babies will all have their genetic profiles sequenced and stored so that for certain crimes, no suspects would be needed in order to attain DNA samples. Investigators could simply install the "fingerprint" into the databank and search for a match. The criminal justice system could allow DNA as evidence showing that someone, genetically, can't help committing certain illegal acts. However, the application of these daunting scientific advances clearly has the potential to infringe upon our individual privacy rights. It is unknown whether society will choose to implement many of the forensic possibilities that these scientific breakthroughs allow. If it does, some day we may be able to execute or exonerate based solely on DNA evidence, or, perhaps, even solely on predisposition. As Omar Khayyam so presciently wrote almost 1000 years ago, life may depend on a single droplet of blood, or even just one hair.

Works Consulted

Connors, Edward, Thomas Lundregan, Neal Miller and Tom McEwen. "Convicted by Juries, Exonerated by Science: Case Studies in the Use of DNA Evidence to Establish Innocence After Trial." U.S. Department of Justice, Office of Justice Programs (June1996).

Lander, Eric S. "DNA on the Witness Stand." Access Excellence @ The National Health Museum (1999).

Liebman, James S. "A broken System: Error Rates in Capital Cases, 1973-1995." The Justice Project (June 2000).


Niezgoda, Stephen and Barry Brown. "The FBI Laboratory's CODIS Program" (July, 2000)

Roberts, Reid.

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