IMAGINE THE FOLLOWING SCENARIOScene: The Highway Motel, #1 Dark Highway, Nowhere Setting: Room #13.The motel manager hears loud voices, a woman screams, and a shot rings out. The manager runs tothe window in time to see the receding lights of a car leaving in a hurry. The door to room #13 hangsopen. The manager runs to the open door to see a man lying face down in a pool of blood. He calls911. The police arrive and begin to examine the crime scene. An apparent homicide, but with noobvious clues as to who committed the crime.Or...?A forensic specialist is called in to examine the crime scene and collect evidence. Even though it looks likethe people involved left no evidence behind, the specialist can use laboratory tests that can tell who wasat the crime scene from a single drop of blood or a lone hair. Is this a science fiction story, or reality?Very much a reality. Testing is routinely done in forensic testing labs across the U.S. and in many otherparts of the world from only a single cell, and sometimes from samples that are decades old. Thereason this is possible is because of DNA. To be able to perform laboratory tests, the specialist needsbiological material to work with. Often, there is very little material left at the scene of a crime, and notin quantities that will allow analysis. To get around this problem, the specialist takes advantage of aprocess that each and every cell in your body uses to divide.The most important part of any cell's life is when it commits to reproducing itself and dividing. Thebasic result of any cell division is the creation of two identical daughter cells from one original cell. Toensure that this happens, DNA replication must have a high degree of specificity and accuracy, thatis, it must copy DNA exactly. To do so, the enzymes involved in DNA replication use the informationalready contained in the existing strands to make new DNA copies. This basic idea - the exactcopying of DNA from a template - is the basis for a new technology that has revolutionized manyareas of science, medicine, and the courts.PCR allows the forensic specialist to specifically amplify, or copy, any region of DNA that he or she isinterested in. PCR is the basis for DNA testing that is currently used in nearly all forensic analysis.In this experiment, you will perform PCR analysis on a single locus, the BXP007 locus, using templateDNAS obtained from a simulated crime scene and a victim. Following PCR, you will run an agarosegel to separate the PCR products, visualize the PCR products, compare them to a simulated ladder ofpossible alleles for this locus, and assign a genotype for the templates. You will then look to see if anyof the suspects' genotype match the crime scene, and see whether you can determine whodunit!Let's examine the DNA evidence and find out who pulled the trigger.172Introduction to PCR- Based Forensics Questions - Introduction1. What kinds of materials obtained from a crime scene might contain DNA?2. Why do you need to perform PCR on DNA obtained from a crime scene?3. What might you see if you ran a DNA sample extracted from evidence on a gel before PCR?4. What is a genotype?Oestions5. What is the difference between an allele and a locus?6. Why do forensic labs analyze non-coding DNA and not genes?Introduction to PCR-Based Forensics173

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Questions - Introduction 1. What kinds of materials obtained from a crime scene might contain DNA? 2. Why do you need to perform PCR on DNA obtained from a crime scene? 3. What might you see if you ran a DNA sample extracted from evidence on a gel before PCR?