TAS2R38 is a single locus on chromosome 7 which controls the ability to taste the bitter chemical PTC (phenylthiocarbamide). The dominant T allele controls the ability to taste and is completely dominant over the recessive allele t.
The locus can be readily amplified using polymerase chain reaction and commercially available primers to yield a 221 bp fragment. A single nucleotide polymorphism (SNP) results in the presence of a Hae III restriction enzyme recognition site in the amplified TAS2R38 gene, allowing cleavage of the dominant T allele fragment into two smaller fragments: 44 bp and 177 bp length. The t allele lacks the recognition site for Hae III.
This allows screening for genotype at the TAS2R38 locus using PCR, followed by restriction enzyme digestion of the product with the restriction enzyme Hae III and agarose gel electrophoresis.
Jamie has a young baby and wants to determine if her previous boyfriend, Byron, is the father, so she enrolled in a genetics and genomics class. Her instructor has the class use PCR to amplify the TAS2R38 locus responsible for tasting PTC. She brings a sample of mucosal tissue from the baby into the laboratory analysis, amplifies the DNA in the thermocycler, and digests it with HaeIII along with her own sample.
A diagram of the resulting ethidium bromide stained gel following agarose gel electrophoresis is shown below. Lanes marked "U" represent undigested DNA and lanes marked "D" are loaded with DNA digested with HaeIII.