The bloggers here at OpenHelix and some of our family and friends decided to do the taste tests. You know the ones. You probably did them in your genetics class. I used them in my introductory biology class at CCSF years ago and had hundreds of the test strips left. So, we thought we’d distribute them to the bloggers and families here and see what the results were. The test strips are for sodium benzoate, PTC and thiourea. There is also a control strip of no taste (but paper). I numbered the strips and sent them to the bloggers and families (so they wouldn’t know what they were tasting, control or otherwise). And here are the results (and some database links to more about the genetics of taste):
First me: I am a walking recessive. A cipher. The ‘uncommon’ allele. In everything. Blond hair, blue eyes, no hair on my mid-digit of my fingers, right thumb on top when clasping hands, unbent little finger and the list goes on. So what do you think the taste test showed?
You guessed it.
I couldn’t taste anything on any paper. Nada. This walking recessive still walks recessively even in taste.
When I gave the PTC paper to my almost 6-year-old daughter (who is adopted btw, of African heritage), the reaction her facial expression seemed to say was “Why in the world would you, the parent who loves and cares for me, give me something so vile and disgusting as that?” To make matters worse, I laughed at the reaction. She was not pleased. But to this day, it still strikes me as odd that other people taste something so drastically strong when I don’t taste anything at all. I find it amusing in a strange way. I apologized and explained it was all for the good of science. I’m not sure she’ll like science much any more.
She also thought the thiourea paper tasted like paint and the sodium benzoate tasted like the sugar “Papa likes” (that’d be the artificial sweetener I put in my tea).
The other OH bloggers?
Mary: SB, sweet (like nutrasweet. PTC, burnt tires (w a lingering aftertaste that keeps on giving). Th, nothing.
Jennifer: SB, mildly sweet. PTC, quite bitter. Th, moderately bitter.
We tested a some others. Scott and Neeraj, the two who post to the OH news and some friends and family, here are our results:
As you see, we got some diverse answers and and all the controls were given a ‘no taste’ rating so we know no one was having any phantom tastes. I also find it interesting that the PTC tastes seem to fall into two main categories (other than the nontasting of the walking recessive): very bitter and metallic.
Well, that was the phenotype. What about the genotype?
Though the genetics of sodium benzoate taste aren’t well described, those of PTC are.
The taste of PTC is affected by the a gene in the TR2 family of “G-protein-coupled receptors” (GPCR). In fact it is TAS2R38 (the link opens a session of the UCSC Genome Browser with that gene). In fact, there are three non-synonymous coding SNPs in this region that form 5 distinct haplotypes in various populations. You can see those three SNPs at HapMap and explore them more at the Genome Variation Server and learn more at OMIM (all link directly to the TAS2R38 gene record at those resources).
The basic conclusion is that the genotypes of these three SNPs affect how PTC is experienced. Homozygotes for the common alleles for each of these three variations taste PTC strongly, heterozygotes not so strongly and homozygous rare alleles not at all. But with five haplotypes, the variation in taste for PTC will be quite diverse and not quite as simple as ‘dominant/recessive,’ but it’s a good lesson in the connection between genotype and phenotype.
Now all we need to do here at OH is genotype ourselves :).