Option 1: Police investigating the scene of a sexual assault recover a large blanket that they believe may contain useful physical evidence. They take it to the laboratory for a test for the presence of semen. The serologist asks if the investigator knows of Respond to one of the following:
anything that might recently have been spilled on the blanket. The investigator reports that an overturned bowl of grapes and watermelon was found on the scene, as well as broken glass that had contained wine. The scientist selects and administers the best test for analyzing that blanket. The blanket shows a positive reaction after three minutes of the completion of the test. What test was probably used and what was the conclusion? Explain your answer.
Option 2: Criminalist Cathy is collecting evidence from the victim of a sexual assault. She places a sheet on the floor, asks the victim to disrobe, and places the clothing in a paper bag. After collecting pubic combings and pubic hair samples, she takes two vaginal swabs, which she allows to air-dry before packaging. Finally she collects blood, urine, and scalp hair samples from the victim. What mistakes, if any, did Cathy make in collecting this evidence?
Option 3: A woman reports being mugged by a masked assailant, whom she scratched on the arm during a struggle. The victim gives the police a good description of her attacker, but she is not sure whether the assailant was male or female. Describe the steps and procedures you might use to determine the sex of the attacker.
Option 4: Police discover a badly decomposed body buried in an area where a man disappeared some years ago. The case was never solved, nor was the victim’s body ever recovered. As the lead investigator, you suspect the body is that of the missing victim. What is your main challenge in using DNA to determine whether it is or is not? How would you go about using DNA technology to test your theory?
Option 5: Define antigens, antibodies, antiserum, and agglutination.
Option 6: Describe the Luminol, microcrystalline, and precipitin tests for blood.
Option 7: Semen is determined by two tests. List them and explain each in detail.
Option 8: Describe the physical evidence to be collected from a rape victim examination and how it is to be collected. Who is to collect this evidence?
Option 9: Briefly describe what DNA is and its structure. What are the restrictions on base pairings?
Application and Critical Thinking
- Police investigating the scene of a sexual assault recover a large blanket that they believe may contain useful physical evidence. They take it to the laboratory of forensic serologist Scott Alden, asking him to test it for the presence of semen. Noticing faint pink stains on the blanket, Scott asks the investigating detective if he is aware of anything that might recently have been spilled on the blanket. The detective reports that an overturned bowl of grapes and watermelon was found at the scene, as well as a broken glass that had contained wine. After the detective departs, Scott chooses and administers what he considers the best test for analyzing the piece of evidence in his possession. Three minutes after completion of the test, the blanket shows a positive reaction. What test did Scott choose and what was his conclusion? Explain your answer.
A: Scott chose the acid phosphatase test, because it is extremely useful in searching for semen on large areas of fabric, such as a blanket. He concluded that the blanket did not contain evidence of semen. First of all, he knew that certain fruit juices, including watermelon, can generate a positive reaction with acid phosphatase testing. However, these juices react much more slowly to the test than semen does. A reaction time of less than thirty seconds is considered a strong indication of semen. Because it took three minutes to obtain a positive reaction, Scott concluded that the positive reaction was caused by the watermelon.
2.Criminalist Cathy Richards is collecting evidence from the victim of a sexual assault. She places a sheet on the floor, asks the victim to disrobe, and places the clothing in a paper bag. After collecting pubic combings and pubic hair samples, she takes two vaginal swabs, which she allows to air-dry before packaging. Finally, Cathy collects blood, urine, and scalp hair samples from the victim. What mistakes, if any, did she make in collecting this evidence?
A: Cathy made four mistakes in collecting evidence. First, she should have placed a paper sheet over the sheet on which the victim disrobed, in order to collect any loose material that may have fallen from the victim or the clothing. Second, she should have placed each item of clothing in a separate bag, instead of placing all of them in the same bag. Third, she should have taken two additional vaginal swabs, smearing them onto microscope slides. Finally, she failed to collect fingernail scrapings from the victim.
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