Inspired by the comments yesterday, here is a compound that was used in early human genetics: phenylthiocarbamide, or PTC:
PTC is one of those molecules with the puzzling properties of tasting bitter to some, and like nothing at all to others. This page gives a good overview:
To some people the chemical substance phenylthiocarbamide tastes intensely bitter while to others it is almost tasteless. The ability to taste this and a number of other chemically related substances is inherited. There are two genes, T for tasting and t for non-tasting. T is dominant in expression over t. This system was one of the first genetically simple systems to be discovered in man; it has therefore been widely applied in population studies, and there are considerable differences between populations in their taster frequencies.
[...]
The ability to taste PTC is present in about 70% of the overall human population, varying from 58% for Australoid peoples to 98% for Native American populations.
It goes on, and on, and on, and is really pretty fascinating reading. When I stumbled upon this awhile back it brought memories back of an intrepid high school biology teacher, doling out little hole-punch size dots of blotter with PTC on them. It's kooky stuff like that, the "here, put this in your mouth, and I'll explain why later" science that gets people excited. I fear the chemical-laden chad might not be as prevalent in classrooms these days, and we're the worse for it. (Your humble author is of the taster phenotype, however, so his memories of the experience might be more vivid than those who just felt like they were munching on normal paper).
Update: I was wrong, wrong, wrong! If you haven't ever tasted (or failed to taste) PTC, you can get some here, for a mere $2. 100 strips, enough for the better part of a year's worth of students, or loads and loads of strangers.
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A few questions:
Do you know the what percentage of Europeans can taste it?
Are there any known correlations between being able to taste the compound and mitochondrial or Y-chromosome haplotypes?
Minor quibble: there is one gene with two alleles (T and t), not two genes.
Speaking of genetically linked tastes, I have no idea what the compound(s) involved might be, but my daughter and I have found numerous other related people who all experience the taste of fresh cilantro (aka coriander) as distinctly soapy and unpleasant. We have no problem with cooked cilantro or coriander seed.
The compounds in cilantro are saponins, whose name comes from the fact that they taste soapy to some people (I'm not one of them).
chezjake - One of the terpenes is an acetate (probably others) so might be a good candidate for degradation after cooking. Chemically the terpenes and the example carbamide are structurally similar and of similar molecular weights. Interesting story.
I was a non-taster. The relief I felt for not having to taste something gross was about as memorable as those who could taste it. I remember being terrified when the teacher presented us with the little strips. He explained the process first, though... I might have been better off if he'd left it a mystery.
The PTC papers are most definitely NOT extinct in the high school classroom... we go through a few hundred of 'em each and every semester. They're cheap and easy to use, and since I'm lucky enough to be a nontaster, I hand them out to the kids and we all "taste" together... while most of them are making horrible faces, I'm chewing on it like a piece of hay and saying, "What? What's wrong?"
Have no fear - we'll keep on doing it!