When Gregor Mendel published his studies of inherited characteristics of pea plants in 1866, he probably didn't know he was starting a sequence of events that would end in 1987 conviction of someone in United States based on DNA evidence. This article discusses history and current status of use of DNA evidence in 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 inherited characteristics of each person. Historically, DNA could only be extracted reliably from clean specimens of blood or other body fluids. Due to recent scientific developments, DNA evidence can be extracted and amplified from a variety of samples, including licked stamps, dental floss, used razors, hair, and even sweaty t-shirts.
The DNA evidence is taken back to laboratory where sample is cleaned and prepared. The DNA is cut into small, manageable pieces using enzymes, and then it is categorized by size using a process known as "gel electrophoresis." We all share some 99.9% of our DNA, but there are specific regions in our DNA that differ. In certain areas, given sequences of bases adenine, thymine, cytosine, and guanine repeat themselves. The sequences, known as variable number tandem repeats, or VNTRs, create a unique personal blueprint that can be used as DNA evidence.
The VNTRs are marked with a radioactive compound that aids in being able to make an x-ray image of DNA sequence. These images, which are DNA evidence ultimately presented in courts, can then be compared to DNA sample collected from a suspect.
The DNA sample from crime scene and suspect are compared at a number