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Dna Testing

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Assignment: DNA Testing James Bunch CRJ311 Forensics Instructor Will Curcio April 9, 2012

This paper will compare and contrast the newest DNA-typing techniques and short tandem repeats (STRs) with previous DNA typing tests. It will detail how DNA is currently used in criminal investigations. Finally, what is the current impact of DNA testing on the criminal justice system and how has DNA revolutionized this system? In April of 1953 Dr’s Watson and Crick announced the discovery of deoxyribonucleic acid, better known as DNA. The scientific world has not been the same. Before the discovery of DNA the investigators could use blood to narrow the list of suspects. With the discovery of DNA we now have a blood “fingerprint”. Identical twins do not have identical finger prints and in some cases they do not have identical DNA (2008, Casselman). This can make the job of the investigator easier. DNA testing began with Dr. Alec Jeffery in 185 he discovered that certain places on the DNA molecule were repeated. He also found that these repeated sequences were unique to each individual. These repeated sequenced areas are known as VNTRs which is an acronym for variable number tandem repeats. The technique Jeffrey used to examine the VNTRs is called RFLP or Restriction fragment length polymorphism. In this technique a restriction enzyme is used to cut the VNTRs (DNA Initiative). RFLP testing has led to PCR or Polymerase chain reaction testing. The PCR test is able to copy a segment of DNA with the help of a DNA polymerase. The coping process is done automatically using the DNA Thermal Cycler. In a short space of time 30 cycles can multiply
DNA a billion fold. The ability of the polymerase to repeatedly duplicate and amplify a
Single strand of DNA has changed the our ability to identify the source of even the smallest amounts of evidence (2011 Saferstein). The newest DNA typing test is called short tandem repeats or STRs. STRs are locations (loci)
Found on chromosome that contains short sequence elements that are repeated. They are important because they found in large quantities. Normal STRs are in repeating sequences of three to seven bases. The entire strand of an STR is small less than 450 bases long. The result is that because of their seize STRs are less adapt to degrade. They can also be recovered from bodies that are severely decomposed. Their small seize makes them the ideal subject of multiplication by PCR. The STRs have been used to indentify DNA found in salvia left on an envelope (2011, Saferstein). STR is extremely sensitive and requires only small amounts. Investigators are currently accepting protocols as low as 125 picograms This means that only 18 cells containing DNA are needed for testing (2011, Saferstein) DNA typing is used in a variety of criminal investigations. The most important tool
That has been developed is the CODIS system. This stands for the combined DNA index system through this system investigators are able to compare DNA recovered from one crime to DNA found at another. All 50 states take part and provide samples. CODIS was developed by the FBI and there are more than 25 countries that participate (2012 Saferstein). Mitochondrial DNA is found in every cell of the body. It is found outside the
The nucleus of the cell and is inherited only from the mother. mDNA testing while very sensitive is also very expensive. The FBI limits the cases they will do this test for.
Since DNA is inherited from the mother, all of the children will have the same mDNA so while this narrows the list it is not as effective as cellular DNA testing
(2011 Saferstein). We leave DNA behind all the time. Therefore theoretically DNA testing could be done for any crime. The cost of the testing limits its uses. One of the most prominent case is the JoBenet
Ramsey case. When we read about this case it becomes a textbook on what not to do. The crime
Scene was not secured. People were allowed to wander all over the house. This caused the evidence that was discovered to be hopelessly contaminated. There was DNA evidence that pointed to both the guilt and innocence of the parents. DNA can be used to prove the innocence of a suspect. It has been used to set people free who were wrongly convicted. In the 1984 rape and murder of Deborah Sykes Darryl Hunt was convicted of the crime and sent to jail. In 1990 it was found that his DNA did not match the sample. Still the DA was not convinced. Finally, in2003 Willard Brown confessed and it was found through CODIS that his DNA matched. Hunt was finally released. A woman claimed she was held captive and raped. The crime scene was through cleaned.
The investigators were able to recover DNA from a vacuum cleaner bag. It was DNA recovered from a fragment of a contact lens. With only 20 nanograms they were able to match the DNA using STRs t the victim and got a conviction (2012 Saferstein). In June of 2005 the capital Beach doughnut shop was robbed. The two robbers wore bandannas over their faces. They were both armed. In the course of the robbery they ran off, leaving a glove and the bandannas. DNA testing in the two items came back tom Demetrious Walker. \
He pled guilty and is awaiting sentencing. (2012 Star). Since the advent of DNA everything has changed. The new DNA tests to not require as big
A sample as they once did. DNA has even changed the way police define biological evidence.
The new tests using epithelial cells have even produced DNA results. There is a new procedure
That is being developed called touch DNA. This is because of a theory that only 18 skin cells will produce a DNA viable sample. They are predicting eventually they will only need one (1)
Cell (2012 Saferstein).

Reference
Casselman Anne (4/3/2008) Identical twins’ genes are not identical Scientific American http://WWW.scientificaerican.com/article.cfm?id=identical-twins-genes-are-not-identical
DNA initiative History of forensic DNA Analysis http://www.dna.gov/basics/analysihistory Man pleads guilty for role in '05 robbery. (2012, April 3). Lincoln Journal Star,B.3. Retrieved April 8, 2012, from ProQuest Newsstand. (Document ID: 2624703921). Saferstein, R. (2011). Criminalistics: An introduction to forensic science (10th Ed.). Upper Saddle River, NJ: Pearson Education, Inc.

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