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DNA Evidence - History and Status

When Gregor Mendel published his studies ofVNTRs, exponentially increasing the
inherited characteristics of pea plants inprobability that a match between the two
1866, he probably didn't know he was startingspecimens is not an error. Statistically an
a sequence of events that would end in theinnocent person would be more likely to win
1987 conviction of someone in the Unitedthe lottery than to be inaccurately convicted
States based on DNA evidence. This articleusing DNA evidence, assuming that the proper
discusses the history and current status ofnumber  of  sequences  is  analyzed.
the use of DNA evidence in the United States.
Where  DNA  Evidence  Stands  Now
How  DNA  Evidence  is  Gathered  and  Used
The first conviction made using DNA evidence
DNA (deoxyribonucleic acid) is a nucleic acidoccurred in Portland, Oregon in 1987. Juries
consisting of two chains of nucleotidesseemed hesitant at first to accept DNA
bonded together in a double helix, and isevidence as conclusive, perhaps because of
responsible for determining the inheritedthe complicated process - which has been
characteristics of each person. Historically,extensively simplified for this article -
DNA could only be extracted reliably fromthat lawyers and specialists had to explain
clean specimens of blood or other bodyto the jurors. The process in its infancy
fluids. Due to recent scientificleft much room for defense attorneys to
developments, DNA evidence can be extractedinsert doubt into the cases against their
and amplified from a variety of samples,clients. However, as science continued to
including licked stamps, dental floss, useddevelop, DNA evidence and technology gained a
razors,  hair,  and  even  sweaty  t-shirts.foothold  in  the  United  States'  courts.
The DNA evidence is taken back to theDNA evidence and associated technologies were
laboratory where the sample is cleaned andthrust into the limelight when a man by the
prepared. The DNA is cut into small,name of O.J. Simpson was accused of killing
manageable pieces using enzymes, and then ithis ex-wife and her associate in 1995. DNA
is categorized by size using a process knownevidence also played a large role in the case
as "gel electrophoresis." We all share someof the disappearance of child beauty queen
99.9% of our DNA, but there are specificJonBenet  Ramsey.
regions in our DNA that differ. In certain
areas, given sequences of the bases adenine,Just as DNA evidence has been used to convict
thymine, cytosine, and guanine repeatpeople of crimes, innocent people wrongly
themselves. The sequences, known as variableaccused have also been freed based on DNA
number tandem repeats, or VNTRs, create aevidence analyzed after the fact. Ten people
unique personal blueprint that can be used ashave been freed from death row in the United
DNA  evidence.States when DNA technology was finally made
available  to  analyze  their  cases.
The VNTRs are marked with a radioactive
compound that aids in being able to make anAt the time of this writing, several states,
x-ray image of the DNA sequence. Theseprisons, and communities are developing
images, which are the DNA evidence ultimatelyprograms to create DNA databases, especially
presented in courts, can then be compared tofrom those considered dangerous felons or
the  DNA  sample  collected  from  a suspect.high risk criminals. The future of DNA
evidence in the United States lies in the
The DNA sample from the crime scene and thehands of legislatures, courts, and
suspect are compared at a number of differentresponsible DNA labs.



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