- Project Portfolio
- About Us
- Connect With Us
- Contact Us
I am a huge supporter of project-based learning. I was pleased when I found an interesting opportunity published in the journal American Biology Teacher. Titled “Tasting Phenylthiocarbamide (PTC): A New Integrative Genetics Lab with an Old Flavor”, this activity-oriented learning experience uses PTC tasting to illustrate an array of genomic concepts.
PTC tasting has been used as an example of a Mendelian trait controlled by a dominant gene. This paper shows how a teacher can go beyond Mendelian genetics to:
- demonstrate pedigree analysis,
- make Hardy-Weinberg calculations,
- determine student genotypes through the use of cleaved amplified polymorphic sequence analysis, and
- encourage students to examine evidence for evolution at the molecular level.
Teach.Genetics, a Genetic Science Learning Centre based at the University of Utah, indicates that many schools have (in their opinion) needlessly banned the use of PTC paper in schools based on toxicity reports. They suggest PTC is no more dangerous than table salt. They include various calculations to justify their stance. Regardless, salt (NaCl) has a median lethal dose (LD50) of 3000 mg/kg whereas PTC is 3 mg/kg. This is not a trivial difference: it is several orders of magnitude.
Here are my questions:
- Were we in Alberta previously far too cautious?
- Are we now being far too imprudent?
- Is it even wise for a teacher to suggest that students taste something described on Wikipedia as being twice as toxic as potassium cyanide? (I’m imagining the hushed tones of the breathless reporter on the evening news as I type this).
Our blog comments are moderated and do not show up immediately. Your email address is not revealed. You can also let me know directly by email or send me a tweet.
You can find me on
While I suspect that some teachers dream of giving a hefty dose of cyanide or other toxic substance to an occasional administrator, it behooves us to think carefully about the benefits versus the risks of using hazardous materials with students, It is always worthwhile to look for alternatives that might be better. A fine example of this is the use of online physics problem-solving. It's far safer to show the effects of increasing the mass of an object when sending the object in a circular path by using a computer than it is to have a carload of teenagers trying to prove the same results driving around a bend at speed.
I am old enough to remember the use of mercury thermometers in class. Although I held and played with mercury as a student (and it didn't hurt me -- I think) no one today would use mercury thermometers because we now have a better idea of the toxicity of mercury (and the potential lawsuits involved for using it!) Digital thermometers are a better choice because they are safer and they have the added benefit of being more accurate than mercury thermometers.
I jokingly referred to cyanide in my initial sentence but HCN is another substance that can be used for the dominant gene test but it's high effectiveness as a rodenticide precludes it from being an acceptable substance in most science classes.
So, given the knowledge that PCT is toxic in surprisingly small doses and given the risks involved in using PCT, I believe we are prudent to avoid it in the classroom. Better to stick with recessive or dominant earwax. It's also more funny to talk about.
Gerry Ward - genomealberta.ca/
Thanks for the comments from the retired teacher.
Here are some additional comments from the G+ Genetics and Genomics Community
(cut and paste this URL if it is not a live link)