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PTC Can you taste bitter?
PCR Lab – PTC Taster
What DNA sequence
are we going to copy?


TAS2R gene
Encodes a PTC taste
receptor (senses a
bitter taste)
The Anatomy of
Taste
Genetics Science
Learning Center
PCR Lab – PTC Taster
What do we do with bitter taste receptors?


Many toxic plants are bitter tasting
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 7
1002 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
TASTERS

Heterozygous – Tt

Homozygous recessive - tt
NON-TASTERS
PCR Lab – PTC Taster
Non-taster PCR
product - 221 bp
Taster PCR
product - 221 bp
SNP – Single
Nucleotide
Polymorphism.
One “letter”
makes a big
difference.
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 - 221 bp
• Can you predict bands for these genotypes?
• TT (PTC strong taster)
• Tt (PTC weak taster)
• tt (PTC non-taster)