PTC - Can you taste bitter? Internet Link – ScienceNow Picky Eaters Video V: Drive Link – ScienceNow Picky Eaters Video

PCR Lab – PTC Taster What DNA sequence are we going to copy? TAS2R gene TAS2R gene Encodes a PTC taste receptor (senses a bitter taste) Encodes a PTC taste receptor (senses a bitter taste)

Genetics Science Learning Center The Anatomy of Taste

PCR Lab – PTC Taster What do we do with bitter taste receptors? Many toxic plants are bitter tasting Many toxic plants are bitter tasting People with high levels of bitter taste receptors are less likely to smoke. People with high levels of bitter taste receptors are less likely to smoke.

PCR Lab – PTC Taster Chance discovery

Background on TAS2R38 Gene (Bitter Taste): 1930’s -- first reported on variation of ability to taste PTC (phenylthiocarbimide) PTC bitter taste has been widely used in Mendelian genetics studies Bitter taste –Controlled by group of bitter taste receptors –Gene family = TAS2R –Bitter taste receptors are TRANSMEMBRANE 7 helical regions that wind through the cell membrane

DNA… TAS2R38: Chromosome bp long

…to Protein Non-tasters differ from tasters at 3 locations in the TAS2R38 gene… Non-taster (t) (AVI) Taster (T) (PAV) Amino acid #: 49 GCA (Alanine)CCA (Proline) Amino acid #: 262 GTT (Valine)GCT (Alanine) Amino acid#: 296 ATC (Isoleucine)GTC (Valine)

Protein picture… Cytoplasmic

PCR Lab – PTC Taster Being a “taster” is a dominant trait Homozygous dominant – TT Homozygous dominant – TT Heterozygous – Tt Heterozygous – Tt Homozygous recessive - tt Homozygous recessive - tt TASTERS NON-TASTERS

PCR Lab – PTC Taster Non-taster PCR product - SNP – Single Nucleotide Polymorphism. One “letter” makes a big difference. Taster PCR product bp

Determing PTC genotype Extract DNA from cheek cells Amplify TAS2R38 region (PTC) using PCR Digest PTC-PCR product with HaeIII –PCR product is 221 bp Taste allele (T) = one HaeIII site –Sizes of 177 bp and 44 bp Non-taste allele (t) = no HaeIII site –Remains uncut bp Can you predict bands for these genotypes? TT (PTC strong taster) Tt (PTC weak taster) tt (PTC non-taster)