Author: Biology Junction Team

 

Who Ate the Cheese?!

Introduction:

DNA isolation from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared with the DNA of a criminal suspect to determine guilt or innocence. This is due to the fact that every person has a different sequence. Scientists use a small number of sequences of DNA that are known to vary among individuals, and analyze those to get a possibility of a match.  DNA is isolated, cut using restriction enzymes and sorted by size by gel electrophoresis. DNA is placed in a gel and an electrical charge is applied to the gel. The positive charge is at the top and the negative charge is at the bottom. Because DNA has a slightly negative charge, the pieces of DNA will be attracted to the bottom. The smaller pieces move more quickly towards the bottom than the larger pieces. The DNA can then be analyzed.

Objectives:

In this simulation you will examine crime scene evidence to determine who is responsible for eating the Queen’s special imported Lindbergher Cheese (yes, the stinky cheese). You will model the process of electrophoresis and DNA fingerprinting.

ROYAL GUARD INCIDENT REPORT

Incident Data Incident Type: Theft Complaint Status Pending DNA results Processed by: Chief Wiggam Other Officers: Officer Li Gase Property Property Code: Rare cheese Owner’s Name Queen Elizabeth Name: Lindbergher Value: $12,000 Burglary Data Method of Entry: Unknown, no evidence of force on doors or windows. Narrative: The cheese was allegedly stolen from the Queen’s sitting room the night before the grand ball. The cheese was listed as a gift from the Manchurian diplomat. Officer Li Gase dusted for fingerprints and found none on the table or doors, the maid claimed that they had been wiped clean earlier. The wheel of cheese was on a platform in the sitting room, and half of it had been eaten. We took pictures of the half eaten cheese and sent it to the lab for further tests. Edna N. Zime, the lab technician said that saliva samples could be taken from the teeth imprints of the cheese that was left behind. Suspect Data Suspect Number: 1 Name: Princess Dubbah Elix Description of Suspicion: The princess was seen entering the sitting room earlier in the evening. She is well known for her love of cheese. Suspect Number 2 Name: Electra Foresis Description of Suspicion: Electra was recently involved in a relationship with the Manchurian diplomat that sources say ended badly. Her motive may have been to sabotage the diplomat’s gift to the Queen. Suspect Number 3 Name: Ada Nine Description of Suspicion: Ada was the maid in charge of cleaning the sitting room. She had access to the cheese. Suspect Number 4 Name: Gene Tics Description of Suspicion: Gene is the leader of the local Cheese-Makers Guild, he may not have wished for Queen Elizabeth to have cheese from anywhere but his own guild. Crime Lab Data Crime Lab Investigator R. Renee Lab Technician Edna N. Zime List of Evidence Received Plastic bag with cheese crumbs List of Procedures Used DNA extraction Polymerase Chain Reaction DNA restriction Analysis Narrative: After receiving the package with the plastic bag marked Crime Scene, the DNA was extracted. Because the sample was so mall, the DNA was amplified using the polymerase chain reaction. We isolated the DNA from the four suspects and compared them to the crime scene DNA using DNA restriction analysis. Results: See attached DNA Results

DNA Evidence Evaluation:

1. Turn your paper strips (DNA sequences) so that the side with the bases is facing you. The restriction enzyme cuts at every point it finds C C G G, always cutting between the C and the G. Label the back of the slips with the suspect number so that you don’t get them confused after cutting. Use scissors to cut the DNA sequence at the C C G G points.

2. Count the number of base pairs (bp) in each piece of DNA that you created. Record the base pair number on the back side of the DNA fragment.

3. Make an enlarged chart like the one shown. Your teacher will give you paper for this. Use a ruler to ensure that the lengths are uniform.

4. Tape your DNA fragments to the chart, using the base pair numbers as a guideline for fragment placement.

5. Compare the crime scene DNA to the suspects and indicate on your chart, which suspect is guilty of eating the cheese.

 

 

 

ANALYSIS:

1. On your chart, label the positive (+) and the negative (-) ends. Circle the suspect’s DNA who matches the DNA at the crime scene and write the name of the suspect.

2. For each of the following tasks performed in the activity, describe what they are actually simulating.

Cutting the DNA into fragments:

 

Taping the DNA onto the large paper:

 

3. For each word below, describe how it relates to DNA Fingerprinting:

Polymerase Chain Reaction:

 

Gel Electrophoresis:

 

Restriction Enzyme:

 

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