01 - Forensic Escape Room: Design Your Own Biotech Adventure
Early fingerprinting analysis involved restriction digestion of the isolated DNA. Following electrophoresis of the digested sample, the DNA is transferred to a nylon membrane during a process known as Southern blotting. Sequence-specific DNA probes are used to visualize the membrane-bound DNA. If the DNA is not digested by the restriction enzyme, the probes will only hybridize to a single DNA segment. If a restriction site occurs within this sequence, the probe will hybridize with multiple bands of DNA. VNTRs are identified when a probe labels DNA at a dissimilar molecular weight. Although RFLP analysis is very precise, it is time-consuming and requires large amounts of DNA. To address these problems, forensic scientists use the polymerase chain reaction (PCR) to produce DNA fingerprints. PCR allows researchers to quickly create many copies of a specific region of DNA in vitro (summarized in Figure 1-1). This technique requires 500-fold less DNA than traditional RFLP analysis and it can be performed in an afternoon. To perform PCR, purified double-stranded DNA is mixed with primers (short synthetic DNA molecules that target DNA for amplification), a thermostable DNA polymerase (Taq) and nucleotides. The mixture is heated to 94°C to denature the DNA duplex (i.e., unzip it into single strands).Next, the sample is then cooled to 45°C - 60°C, allowing the primers to base pair with the target DNA sequence (called “annealing”). Lastly, the temperature is raised to 72°C, the optimal temperature at which Taq polymerase will extend the primer to synthesize a new strand of DNA. Each “PCR cycle” (denaturation, annealing, extension) doubles the amount of the target DNA in less than five minutes. In order to produce enough DNA for analysis, twenty to forty cycles may be required. To simplify this process, a specialized machine, called a “thermal cycler” or a “PCR machine”, was created to rapidly heat and cool the samples. ESCAPE ROOM SCENARIO Monica Homewood has been arrested as the main suspect in the murder of her husband, Bryce Home- wood. She has been questioned multiple times and continues to plead innocent to the crime. Monica’s lawyer is trying to prove her innocence and has convinced the Charleston Police Department to further investigate the crime scene. You are the best forensic analyst that money can buy in Charleston. Your job is to determine if the evidence collected at the crime scene contains blood, what blood type the blood evidence is, and to use DNA fingerprinting to determine who committed the crime. Will your forensics skill help prove Monica’s innocence? The following information and evidence are required for your forensic assessment of the crime.
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