DNA Profiling in the Courtroom
A Lab CIBT Exercise in Molecular Biology
Students will cut DNA with restriction enzymes. The DNA fragments will be separated electrophoretically on an agarose gel. The results will simulate a DNA profile. Students can learn how this type of evidence is prepared and interpreted.
Honors and Advanced Placement Biology.
This experiment will take four to five standard periods to complete. Use the first period practicing with the micropipettors and labeling tubes for the upcoming restriction digest. Use the second period setting up restriction digests, and pouring agarose gels. After a period of incubation at 37°C (can be many hours or even overnight) the digests can be transferred to a freezer. When set, the gels can be thoroughly wrapped in saran wrap and placed in the refrigerator until needed. The third period is for adding dye to the samples and loading the gel for electrophoresis. Some students may be able to observe the beginning of the electrophoresis, while some will be loading their gels right to the end of the period. Teachers can do the staining and destaining, or a few students can return to the classroom for brief periods (5 - 10 minutes each time) to do this part. The fourth period is for photography and analysis of the gels. A double period without a break) for the second lab day makes for a smoother experience. Use some of the additional time in the first period for discussing background material (in this case, leave the labeling of tubes for the second period). Use the remaining time of the double period (after the digests are set up and the gels poured) for much needed lecture/discussion.
(Complete kits are available from many suppliers for activities of this type)
- DNA samples (4 µg of each of 3 different DNA samples / pair) - store the DNA samples and enzymes in the freezer until ready to use!
- 10X restriction enzyme buffer (12 µl / pair)
- HindIII (6 µl / pair) - store the enzymes in the freezer until ready to use!
- HindIII l DNA (size standard; 2.0 µg / pair) - store the DNA samples and enzymes in the freezer until ready to use
- agarose (1 g / 2 pairs)
- 1X TBE (gel running buffer) (1 liter / 2 pairs)
- 5X loading dye (60 µl / pair)
- Carolina Blu (TM) (Carolina Biological cat #21-7300; $7.95/250ml - 2007 catalog) DNA Stain (250 ml / pair)
- sterile water (0.2 ml / pair)
- type 667 Polaroid film (available from Carolina Biological Supply Company 21-3679, $58.50 price from 2007 catalog) per 16 exposures; need 1 exposure per student)
- masking tape
- microfuge tubes (6 / pair)
- pipette tips (1 box small for P20 and P200 pipetmans / pair
- staining trays (1 / 2 pairs)
- beakers for waste
- beakers for ice
- safety glasses
- crushed ice
- 3 cycle semi-log paper (ruled in centimeters; 1 / student)
- 4 liters of distilled water per 2 gels, or 8 liters per 4 gels (1 kit)
- centimeter rulers (1/pair)
Price: No Charge
Jim Blankenship, Cornell University, Ithaca, NY
Mary Colvard, Cobleskill High School, Cobleskill, NY
Glenn Simpson, Victor High