General PLTW Document



Problem 8.3.3 Murder Mystery: Suspect IdentificationIntroductionIn the previous assignment, you learned that skin cells were discovered under the murder victim’s fingernails. The medical examiner believes that this could be evidence that a struggle occurred before the murder and therefore collected the cells for further analysis. This DNA is considered to be evidence from the crime scene. The medical examiner cautioned that the skin cells could belong to the victim. The time of death determined by the victim’s body temperature helped the police narrow down the list of suspects to two men who knew the victim, had a possible motive, and had a window of opportunity to commit the crime that would correspond with the estimated time of death. Suspect 1 is the elevator operator’s roommate and was in the process of moving out of their shared apartment because of a long standing dispute over rent payment. Suspect 2 is an employee at the hotel and told police that he was dating the victim’s girlfriend until recently but that he did not hold a grudge against the victim.You have been supplied with the following samples of DNA:Suspect 1Suspect 2VictimEvidenceThe police have asked you to compare the samples of DNA and submit a report identifying which suspect should be charged with the crime. You must have sufficient evidence to support your charges before an arrest can be made. You must also prove that the evidence DNA does not belong to the victim.In this problem you will use gel electrophoresis to analyze DNA from two suspects, the victim, and DNA from the crime scene to identify which suspect should be charged with the crime.EquipmentLaboratory journalPencilCarolina Exploring Electrophoresis and ForensicsSuspect 1 DNASuspect 2 DNAVictim DNAEvidence DNAAgaroseTBE bufferCarolina BLU? final stain solutionGel box, comb, and electrode setSyringes, tubing, and yellow tipsCarbon fiber sheetLab instructionsElectrophoresis Instructions handoutGlovesProtective eyewearProcedurePart 1: DNA FingerprintingDNA fingerprinting is the process of identifying differences in the DNA of individuals. This can be done with gel electrophoresis, a process that separates segments of DNA cut according to DNA sequences that are unique among individuals. Using this technology the DNA fingerprint of an individual can be compared to that of a sample found at a crime scene. Follow the steps below to learn more about DNA fingerprinting and gel electrophoresis.As a class or individually, view the video “How does DNA fingerprinting work?” at the Naked Science Scrapbook site. the article “Can DNA Demand a Verdict?” at the Learn Genetics website and answer the following questions. The article can be found at: percentage of genetic material is the same in everyone?Where can DNA evidence be found at a crime scene?What procedure does The National Research Council recommend to reduce human error?What other evidence must be taken into consideration in addition to DNA evidence?To the right of the article are the steps of forensic DNA analysis. Use this graphic to draw a sketch for the following steps. For Step 7 draw the bands shown in green on the website.Forensic DNA Analysis StepDrawingStep 1: Collect evidence from the crime scene.Step 2: Isolate DNA from an evidence sample.Step 3: Cut the DNA into fragments using specialized protein “scissors” called restriction enzymes. For every person, the sizes of the cut fragments are unique – except for identical twins.Step 4: Separate the negatively charged DNA fragments in a gel by passing an electric current through it.Step 7: Compare the fragment profile of the evidence DNA with those of the suspects and victim to see if they match.Look at the image in Step 7. Based on the DNA analysis of the gel electrophoresis, which suspect would you identify as the culprit? Explain.Part 2: DNA Gel ElectrophoresisFollow the instructions below to run an analysis of the DNA collected from the crime scene, victim, and suspects.Obtain the Electrophoresis Instructions handout and workstation supplies. Follow the instructions on the Electrophoresis Instructions handout to complete the experiment.After you have obtained your results, either take a photo of the stained DNA bands and attach below or draw a picture of your observations.-3238501968500ConclusionCompare the evidence DNA to the DNA from the two suspects. Which suspect is guilty? pare the DNA evidence to the victim’s. Was the evidence DNA contaminated with the victim’s DNA? Explain.Write a report to the police citing evidence for why the particular suspect should be charged with the crime. You must cite evidence including the time of death, cause of death, and DNA analysis. Your teacher may require you to present this report to a police representative. This report will be evaluated with the Murder Mystery Report Rubric. ................
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