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DNA Evidence - History and Status

When Gregor Mendel published his studiesincreasing the probability that a match
of inherited characteristics of peabetween the two specimens is not an
plants in 1866, he probably didn't knowerror. Statistically an innocent person
he was starting a sequence of eventswould be more likely to win the lottery
that would end in the 1987 conviction ofthan to be inaccurately convicted using
someone in the United States based onDNA evidence, assuming that the proper
DNA evidence. This article discusses thenumber of sequences is analyzed.
history and current status of the use ofWhere DNA Evidence Stands Now
DNA evidence in the United States.The first conviction made using DNA
How DNA Evidence is Gathered and Usedevidence occurred in Portland, Oregon in
DNA (deoxyribonucleic acid) is a nucleic1987. Juries seemed hesitant at first to
acid consisting of two chains ofaccept DNA evidence as conclusive,
nucleotides bonded together in a doubleperhaps because of the complicated
helix, and is responsible forprocess - which has been extensively
determining the inheritedsimplified for this article - that
characteristics of each person.lawyers and specialists had to explain
Historically, DNA could only beto the jurors. The process in its
extracted reliably from clean specimensinfancy left much room for defense
of blood or other body fluids. Due toattorneys to insert doubt into the cases
recent scientific developments, DNAagainst their clients. However, as
evidence can be extracted and amplifiedscience continued to develop, DNA
from a variety of samples, includingevidence and technology gained a
licked stamps, dental floss, usedfoothold in the United States' courts.
razors, hair, and even sweaty t-shirts.DNA evidence and associated technologies
The DNA evidence is taken back to thewere thrust into the limelight when a
laboratory where the sample is cleanedman by the name of O.J. Simpson was
and prepared. The DNA is cut into small,accused of killing his ex-wife and her
manageable pieces using enzymes, andassociate in 1995. DNA evidence also
then it is categorized by size using aplayed a large role in the case of the
process known as "gel electrophoresis."disappearance of child beauty queen
We all share some 99.9% of our DNA, butJonBenet Ramsey.
there are specific regions in our DNAJust as DNA evidence has been used to
that differ. In certain areas, givenconvict people of crimes, innocent
sequences of the bases adenine, thymine,people wrongly accused have also been
cytosine, and guanine repeat themselves.freed based on DNA evidence analyzed
The sequences, known as variable numberafter the fact. Ten people have been
tandem repeats, or VNTRs, create afreed from death row in the United
unique personal blueprint that can beStates when DNA technology was finally
used as DNA evidence.made available to analyze their cases.
The VNTRs are marked with a radioactiveAt the time of this writing, several
compound that aids in being able to makestates, prisons, and communities are
an x-ray image of the DNA sequence.developing programs to create DNA
These images, which are the DNA evidencedatabases, especially from those
ultimately presented in courts, can thenconsidered dangerous felons or high risk
be compared to the DNA sample collectedcriminals. The future of DNA evidence in
from a suspect.the United States lies in the hands of
The DNA sample from the crime scene andlegislatures, courts, and responsible
the suspect are compared at a number ofDNA labs.
different VNTRs, exponentially



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