Forensic DNA Amplification: Who Done It
A CIBT Lab Exercise in Molecular Biology
Within the last two decades extensive research has been focused on biotechnology. It has now become routine to purify DNA and isolate specific genes even though in the early 1970s this would have been considered good material for a science fiction novel. The development of the Polymerase Chain Reaction (PCR) allows incredibly small amounts of DNA to be amplified into a quantity that can be studied in the laboratory. The technology has had a profound impact on the field of forensics. It is now possible to isolate a minuscule sample of blood, semen, or even a hair follicle, to amplify the DNA in the sample, to analyze the amplified DNA, and to compare the DNA sample to DNA obtained from an individual suspected of committing a crime. DNA evidence is now commonly used in criminal cases and also has widespread use in paternity investigations.
In this activity, DNA is collected from oral epithelial cells and amplified by PCR. The PCR-generated fragments of DNA are then separated on the basis of size using agarose gel electrophoresis. The results of the experiment are then photographically documented.
The activity is designed to be a murder investigation. Each one of the participants is a suspect in the crime. Within each group of 6-8 suspects, there lies a murderer. The bands of DNA obtained after amplification of DNA isolated from the evidence at the crime-site are compared to the amplified bands of DNA isolated from cheek cells from each suspect. The banding pattern of the murderer will match the banding pattern of the evidence.
A.P. Biology and Teacher Workshops.
Four lab periods. You will need to devote one class period to discussion and planning. The extraction of DNA and initiation of the PCR reactions will take a second lab period. The DNA Amplification (~ 3 hours) can be done outside of class time. The third lab period will be devoted to the preparation of agarose gels and the loading of amplified samples onto the gels. DNA electrophoresis will take 2 hours and can be completed by the teacher outside of class time. The teacher will then stain and destain the gels outside of class time. The fourth lab period will be devoted to photographic documentation and analysis of the results.
Materials shared by everyone:
- Boiling water bath.
- Forensic kit - available from Carolina Biological Supply Company (2700 York Rd., Burlington, NC 27215), see supply pages for details. Cost is approximately $121.00 in 2007 catalog.
- A Thermal Cycler.
- 4 Gel electrophoresis chambers, trays, combs, and power supplies.
- Photographic apparatus including a UV transilluminator, camera, red filter, protective eye wear, and Polaroid type 667 film.
- Clinical centrifuge equipped with a rotor that accepts 15 ml conical screw cap tubes.
Materials for each Team of students:
- microcentrifuge tube racks
- disposable 15 ml conical orange cap centrifuge tubes containing 10 ml 0.9% NaCl (1 per student)
- white microcentrifuge tubes (1 per student)
- blue microcentrifuge tubes (1 per student)
- 2-20ul micropipettor
- 2 boxes of sterile tips for micropipettor
- sterile disposable graduated transfer pipettes
- beakers containing ice
- 1.5 grams of Agarose
- 1 liter 1X TBE buffer (may be purchased from Carolina Biological Supply Company)
- 1 thermometer
- latex gloves
- 1 resealable plastic storage bag.
Price: No Charge
Jim Blankenship, Cornell University, Ithaca, NY
Rita Calvo, Cornell University, Ithaca, NY
Glenn Simpson, Victor High School, Victor NY