PTC (PHENYLTHIOCARBAMIDE ) Ability for some people to taste while others cannot was accidentally discovered in the 1930s. Today we know that the ability to taste PTC (or not) is conveyed by a single gene that codes for a taste receptor on the tongue. The PTC gene, TAS2R38, was discovered in 2003. There are two common alleles of the PTC gene,and at least five rare forms. One of the common forms is a tasting allele (PAV), and the other is a non-tasting allele (AVI). 99% of non-African people have one of these two alleles. The others vary in how intensely they perceive PTC. Some of the frequencies of the non-tasting gene in different races have been reported as follows: Aboriginal Australian and New Guinea – 0.707 North American white population - 0.550 Japanese - 0.266 Jewish (Ashkenazic) - 0.524 India - 0.581 Brazilian indigenous - 0.111. In the North American white population approximately 20 per cent are homozygous tasters, 50 per cent are heterozygous tasters, and 30 per cent are nontasters. YOU – TT = 7/14 = 50%, Tt =3/14 = 22%, tt = 4/14 = 28% A recent study found that PAV/PAV individuals rated vegetables like broccoli, watercress and kale as 60% more bitter than AVI/AVI individuals. PAV/AVI individuals gave them an intermediate score. Even among the tasters of PTC, unless the chemical has dissolved in the taster's own saliva, it is tasteless. If PTC is dissolved in some one else's saliva or in water and placed upon the dry tongue of a taster, it cannot be tasted.

333 amino acids AVI (no-taste): PAV (taste): PAV and AVI are named based on the different amino acids present at three different positions in the resulting protein (333 total aa) – positions 49, 262 and 296 in the “TAS2R38” receptor protein on chromosome 7. P=proline, A=alanine, V=valine, I=isoleucine PAV= proline-alanine-valine AVI = alanine-valine-isoleucine 333 amino acids AVI (no-taste): 1 mltltrirtv syevrstflf isvlefavgf ltnafvflvn fwdvvkrqal snsdcvllcl 61 sisrlflhgl lflsaiqlth fqklseplnh syqaiimlwm ianqanlwla aclsllycsk 121 lirfshtfli claswvsrki sqmllgiilc scictvlcvw cffsrphftv ttvlfmnnnt 181 rlnwqikdln lfysflfcyl wsvppfllfl vssgmltvsl grhmrtmkvy trnsrdpsle 241 ahikalkslv sffcffviss cvafisvpll ilwrdkigvm vcvgimaacp sghaailisg 301 naklrravmt illwaqsslk vradhkadsr tlc PAV (taste): 1 mltltrirtv syevrstflf isvlefavgf ltnafvflvn fwdvvkrqpl snsdcvllcl 241 ahikalkslv sffcffviss caafisvpll ilwrdkigvm vcvgimaacp sghaavlisg

Campbell et al, 2011 *some of these are shared with chimpanzees who have the same gene at the same place.

Sodium Benzoate – used as a food preservative. People perceive it as either: tasteless salty sour bitter sweet While PTC and sodium benzoate tasting are controlled by different genes, their combined presence or absence appears to influence taste. “Fox found “that after testing about 1500 people that practically every possible combination of tastes could be found except that in which PTC was tasteless and sodium benzoate bitter. The more numerous cases were (giving the tastes in the order: PTC-sodium benzoate): (1) bitter-salty, (2) bitter-sweet, (3) bitter-bitter, (4) tasteless-salty. It further appears the ‘bitter-salty’ group finds the taste of a variety of foods which may be considered controversial (sauerkraut, buttermilk, turnips, spinach, etc.) more attractive than average, whereas those who are in the ‘bitter-bitter’ group like the taste of such foods less than average.”

Thiourea PTC is a type of thiourea. Not sure what this strip contains.  It is likely to be the related compound propylthiouracil (PROP). So, a different chemical that is detected using the same receptors

Supertasters! <15 papillae = “relaxed taster” - 1/4 15-35 papillae= “average taster” – 1/2 >35 papillae = “super taster” - 1/4

  PTC TU SB Jacob GROSS PAV/PAV gross salty Daddy Mommy Noah sweet

Easily observed variations in humans: •Tongue Rolling: People who can roll their tongues into a tube have at least one R allele (R–) and those who can’t are rr. •Widow’s Peak: If your hairline forms a “V” on your forehead, you are W– and if your hairline is straight, you are ww. •Ear Lobes: If your earlobes are detached, you have at least one E (genotype E–), but if they are attached, you are ee. •Little Finger: Hold your hand out with fingers together. If the end joint of your little finger bends in, you are F–. If it is straight, you are ff. •Hitchhiker’s Thumb: Hold out your hand like you’re hitchhiking. If your thumb bends back at quite an angle, you are H–. If your thumb is fairly/nearly/almost straight, you are hh. •Mid-digital Hair: Look closely at the middle segments (not knuckles or joints) of all of your fingers to see if any of them have hair growing on them (If it’s a finger you use a lot, the hairs may be worn down to stubble, so look closely.). If there is any hair on any of them, you are D’. If all your middle segments are totally bald, you are dd. PTC tasting Gender – XX, XY Even just considering these 7 traits there are 128 different combinations of these traits.

In humans with 23 pairs of chromosomes, a gamete would have 2^23 = 8,388,604 possible combinations of chromosomes (each bearing numerous genes) from that parent. Any couple could have 2^23 × 2^23 = 70,368,744,177,644 (70 trillion) different possible children, based just on the number of chromosomes, not actual genes. Thus, based on the number of chromosomes, the chance of 2 siblings (other than identical twins) being exactly identical is 1/70 trillion. To make things even more complex, crossingover, or exchange of segments between homologous chromosomes during synapsis, can add further variation.