02 DNA Extraction Lab Rep - DNA Extraction Chad K Bush 27...

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DNA Extraction Chad K. Bush 27 October 2005 Bryant Bowen
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ABSTRACT The purpose of this experiment is to identify which of two rape suspects most likely committed the rape. Two samples of biological material were obtained from the scene of the crime: E1 was a sample of semen collected from the vagina of the rape victim, and E2 was a sample of biological material collected from the rape victim’s clothing. Two DNA samples were also obtained from each of the two suspects. After the extraction of the deoxyribonucleic acid (DNA), it is broken apart by restriction fragment length polymorphism and analyzed by gel electrophoresis. A restriction enzyme is used to cleave the DNA, which is then prepared in an agarose gel for electrophoresis. The DNA of suspect #1 (S1) was found to be a probable match with the DNA from crime scene sample #1 (E1). However, the DNA from suspect #2 (S2) was found not to match with either of the crime scene samples, which effectively exonerated him. Also, the crime scene sample #2 (E2) of biological material collected from the rape victim’s clothing did not match with the semen collected from the rape victim’s vagina or the biological material from S1. INTRODUCTION Each human cell contains 6 x 10 9 base pairs of deoxyribonucleic acid (DNA). Some of this codes for actual proteins (in areas of DNA called exons), but of these six billion base pairs, a large portion are non-coding intron sequences that are free to mutate extensively (Kimbell 125). The number of introns in transcribed RNA ranges from zero in histone genes to an estimated 2.5 million bases in some protein genes (Bergemen 6). Some genes have over 75 introns and only 1
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0.5 per cent (about 11,000 bps) of the gene consists of exons. With this extraordinarily small probability that any two individuals would have an exact match of their base pairs, DNA is unique to each organism, and DNA typing has become an extremely important method for the identification of one individual and for the linking of that individual to samples collected from crime scenes in forensic science. Restriction enzymes have been shown to be indispensable tools in DNA typing and have helped to contribute to the progress of genetic forensics and molecular biology (Roberts 2005). These restriction enzymes cleave DNA at certain points along the base sequence, so that each DNA molecule forms many parts of different sizes and masses (by the process of restriction fragment length polymorphism). These DNA chunks or alleles, when in solution, carry a negative charge. If they are stained and placed in a gel electrophoresis chamber well and an electric current is passed through the gel, the DNA will form bands of alleles as certain fragments migrate toward a positive charge.
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