DNA Evidence - History and Status

When Gregor Mendel published his studies of inherited characteristics of pea plants in 1866, he probably did not know he was starting a sequence of events that would end in the 1987 conviction of someone in the USA based on DNA evidence. This Report discusses the history and present status of the use of DNA evidence in the United States.

How DNA Evidence is Gathered and Used

DNA (deoxyribonucleic acid) is a nucleic acid consisting of two chains of nucleotides bonded together in a double helix, and is responsible for determining the inherited traits of each individual. Historically, DNA could only be extracted reliably from clean specimens of blood or other body fluids. Because of recent scientific advancements, DNA evidence can be extracted and amplified from an assortment of samples, such as licked stamps, dental floss, used razors, hair, and even sweaty t-shirts.

The DNA evidence is taken back to the lab where the sample is cleaned and ready. The DNA is cut into small, manageable pieces using enzymes, and it is categorized by size using a procedure called"gel electrophoresis." Most of us share some 99.9% of our DNA, but there are certain areas within our DNA that differ. In certain locations, given sequences of the bases adenine, thymine, cytosine, and guanine repeat themselves. The sequences, known as variable number tandem repeats, or VNTRs, create a unique personal blueprint which can be utilised as DNA evidence.

The VNTRs are indicated with a radioactive chemical that assists in being able to generate an x-ray picture of their DNA sequence. These pictures, which are the DNA evidence ultimately presented in courts, can then be compared to the DNA sample collected from a defendant.

The DNA sample from the crime scene and the defendant are compared in several different VNTRs, radically increasing the likelihood that a match between the two specimens isn't an error. Statistically an innocent person will be more likely to win the lottery than to be inaccurately convicted using DNA evidence, assuming that the appropriate number of sequences is analyzed.

Where DNA Evidence Stands Now

The first conviction made with DNA evidence happened in Portland, Oregon in 1987. Juries appeared reluctant at first to take DNA evidence as conclusive, possibly due to the complicated procedure - that has been simplified for this article - which attorneys and specialists had to explain to the jurors. The procedure in its infancy left much space for defense lawyers to add doubt into the cases against their clients. However, because science continued to grow, DNA technology and evidence gained a foothold in the United States' courts.

DNA evidence and associated technologies were thrust into the limelight when a guy by the name of O.J. Simpson was accused of murdering his ex-wife and her partner in 1995. DNA evidence also played a huge part in the event of the disappearance of child beauty queen JonBenet Ramsey.

As DNA evidence was used to convict people of crimes, innocent individuals wrongly accused have also been freed based on DNA evidence examined after the truth. Ten individuals have been freed from death row in the United States when DNA technology was eventually made available to examine their instances.

At the time of this writing, many nations, prisons, and communities are developing applications to create DNA databases, particularly from people considered dangerous felons or higher risk criminals. The future of DNA evidence in the USA lies in the hands of legislatures, courts, and accountable DNA labs.