| Case: Bt Corn | Cannabis Case A | Cannabis Case B |
Cannabis cases contributed by Eric Ribbens, WIU, and Ethel Stanley, BioQUEST Curriculum Consortium
Case: Bt Corn
Background: A significant proportion of the corn grown in the U.S. has been genetically modified to contain the crystal toxin gene from Bacillus thuringiensis (Bt corn). The protein translated from this gene is toxic to caterpillars and other larval stage insects. When these insects eat leaf tissue containing the toxin protein, it causes the lining of their digestive tract to deteriorate, eventually killing the insect. There are several versions of the Bt protein. Any that are in the human food supply are tested by the FDA for safety. However, several years ago corn used for human food was contaminated with a Bt protein that had not been approved for human consumption (known as Starlink). This strain of the protein, Cry9C, showed allergen potential in preliminary tests and was being analyzed further. Although no one was apparently harmed by consuming this corn, this incident resulted in more thorough testing of corn prior to its use in human food.
Case description: As a lab technician for a genetic testing company, your job is to determine whether corn samples contain any genetically engineered corn. A corn farmer, Mr. Keller, has hired your company to test his corn. Mr. Keller does not grown any genetically modified corn, but a local elevator has rejected his corn saying that is contaminated with Bt corn.
Procedure: There are three batches of corn to test, each with a different number of samples. Choose one batch to test and use PCR with primers that will amplify any Cry genes present. The primers also contain a primer set that will amplify a portion of the 16SrRNA from corn as a positive control. Run the PCR products on a gel. Report your results to Mr. Keller.
- Did any of the samples contain the the Bt gene?
- How many samples should be tested in order to get an accurate result?
- How could Mr. Keller’s corn be contaminated if he did not plant Bt corn?
- Is the corn that tested positive for Bt safe for human consumption?
Bioinformatics: Which version of the Cry gene is present in the corn samples you tested? Use BLAST to identify the sequence of the PCR product. Click on the gel fragment from one of the samples that is positive for the Bt cry gene. The sequence of that DNA should be visible in the lower window (if not, check the Sequence box above the window). The entire sequence, just a portion containing the repeat region, can be sent for BLAST analysis. See the BLAST tutorial for more detailed instructions. Should this corn be allowed to enter the human food supply?
Cannabis – hemp vs. drug
Background: Arizona has legalized growing and selling hemp. Hemp is a subspecies of Cannabis sativa, but instead of selecting for high THC levels (the chemical associated with marijuana drug use) hemp growers have chosen varieties that produce long strands of fiber. Hemp is easier to grow than cotton in some areas, and is becoming more popular as a fiber source. However, because the THC-containing varieties of Cannabis are illegal to grow or sell in Arizona, the Drug Enforcement Agency (DEA) has been vigilant about making sure that no one takes advantage of the new law.
Case A. George
The Arizona state DEA has arrested George Malkay. George has a record of drug abuse, but claims he is innocent. He grows hemp, which is legal. However, the DEA claims they found 6 bags of dried leaves in his warehouse, bags they think contain high-potency marijuana that, according to an informant, came from Guatemala. George’s lawyer has hired your genetic testing company to test his samples. You have researched Cannabis, and found that several regions with small tandem repeats (STRs) have been identified in the genome. While you cannot directly measure whether a plant is hemp or drug by analyzing these STRs, it is quite possible to make inferences about geographic differences.
Procedure: You have been given 6 samples to test, and have isolated DNA from these samples. Use primers that amplify regions of Cannabis DNA with small tandem repeats (STRs) to carry out PCR tests on the samples and run a gel with the PCR products. The length of the STRs, as indicated by the band patterns on the gels, identify related varieties. Note that there are eight different primer sets that amplify different STR regions that you can use for individual PCR tests, or a file containing all of the primers that you can use for multiplex PCR. Explain the results of your testing to George’s lawyer.
Case B. Bob
Bob Propson is a farmer who has become convinced hemp is worth growing. The DEA, in a routine inspection, collects six samples from his farm. Your genetic testing company has been contracted to test these sample, and it is your job to carry out the tests. You have researched Cannabis, and found that several regions with small tandem repeats (STRs) have been identified in the genome. While you cannot directly measure whether a plant is hemp or drug by analyzing these STRs, it is quite possible to make inferences about geographic differences.
You have isolated DNA from these samples. Use primers that amplify regions of Cannabis DNA with small tandem repeats (STRs) to carry out PCR tests on the samples and run a gel with the PCR products. The length of the STRs, as indicated by the band patterns on the gels, identify related varieties.
- Are all of Bob’s samples from Arizona?
- This is a historical case. What is the current status of Cannabis legalization in the United States?