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 Laura Smith has been arrested for being the main suspect in the murder of her husband, Jeremy Smith. She has been questioned multiple times and continues to plead innocent to the crime. Laura’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 blood 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 Laura’s innocence? The following information may help you with your forensic assessment of the crime. On Saturday night, police dispatch received a distressed phone call from a woman in her mid-30’s, claiming to have found her husband dead in their kitchen upon returning home. Dispatch sent officers to the scene shortly after. Clay, the local police sheriff, was called down to the murder scene at the small suburban condo in Charleston, South Carolina. When he arrived at the condo, Clay found a deceased man in the kitchen. There was a major head laceration on the deceased man. Upon initial inspection of the scene the following primary evidence was collected: glass shards (from a broken bottle of red wine) with what appears to be blood splatter on the kitchen table (Sample 1), a knife near the table with apparent blood on it (Sample 2), potential blood spatter on the hardwood floor near the kitchen table (Sample 3), and a wine glass with women’s lipstick on it. Clay and his crime scene investigators collected the evidence from the scene and the coroner was able to identify the body as Jeremy Smith. Jeremy Smith was a 32 year old man, who was married to 33 year old Laura Smith. Laura was the dis- tressed woman from the police dispatch phone call. When questioned about her whereabouts during the crime, she claimed to have gone to an urgent care to take care of a deep wound she obtained. Laura insists that she accidentally cut herself while cooking dinner with Jeremy. Clay and his partner Amy, questioned the couples’ neighbors. Most of the neighbors complained about their constant arguments. Their fights often disrupted the peaceful neighborhood. However, neighbors also noted that Jeremy was also constantly fighting with the HOA president, Sarah Ann. She is known for being a stickler on the HOA rules and ever since the Smiths moved in, there have only been fights between Jeremy and Sarah. The meeting notes from the HOA meetings prove that the two have a history of being verbally aggressive towards each other.
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