5BBG0203 Human and Molecular Genetics A 2023-2024 Practical. Analysis of polymorphisms in the human PTC taste receptor gene TAS2R38 1.0. Introduction The ability to taste phenylthiocarbamide (PTC), a bitter tasting compound is associated with the gene TAS2R38 which is genetically inherited and exhibits polymorphisms (Blaskeslee, 1932). These polymorphisms are single nucleotide and result in amino acid variation causing the formation of different haplotypes. The PTC taste receptor gene is composed of eight haplotypes which are DNA variants found on the same chromosome at three different sites (Kim et al. ,2003). The frequency within different populations is shown in Table 1. Here the highest two frequencies make up the most common genotype as they are inherited together. It is clear from the table that PAV and AVI are uniformly the most common haplotypes. Therefore across all populations the most common genotypes are PAV/PAV,AVI/AVI and PAV/AVI. All other haplotypes have extremely low frequencies and are rarely seen. The commonality of results across all populations would suggest that through natural selection pervasive pressures have allowed a select few alleles to prevail, however recent studies (Risso, D. S. et al, 2016) actually show signs of balancing selection despite this there was no signs of recent deviation from neutrality suggesting that the current pattern of variation has been influenced by demographic factors. Table 1. Allele frequencies of the eight TAS2R38 haplotypes in human populations (adapted from Rizzo et al. 2016). Population All Africans Asians Europeans Americans PAV 0.5076 0.5076 0.6451 0.4566 0.6861 AVI 0.4270 0.3518 0.3531 0.4922 0.2669 AAV 0.0248 0.0061 0.0000 0.0356 0.0226 AVV 0.0032 0.0008 0.0017 0.0049 0.0000 PAI 0.0018 0.0000 0.0000 0.0032 0.0000 PVI 0.0007 0.0015 0.0000 0.0003 0.0019 AAI 0.033 9 0.132 2 0.000 0 0.005 5 0.022 6 PVV 0.0010 0.0000 0.0000 0.0017 0.0000 2.0. Aims The aim of this practical is to delve into the analysis of the TAS2R38 gene, determining the distribution of haplotypes within a diverse populations of students from different ethnic backgrounds and establish whether the distribution of these haplotypes truly is uniformal 1
across different populations. And through this possibly explore underlying factors for this broad spectrum of PTC sensitivity. 3.0. Results and discussion 3.1. PCR amplification of the TAS2R38 gene from the human genomic DNA of one individual The written results and discussion for 3.1. goes here (delete this instruction in final version). Figure 1. Amplification of the TAS2R38 gene from human genomic DNA. Lane 1. 1 kb plus. Lane 2. Tube 1 purified PCR 1 for gel. Lane 3. Tube 2 purified PCR 2 for gel . Lane 4. Tube 3 PCR 3 for gel Lane 1 Lane 2 Lane 3 Lane 4 Invitrogen 1 kb plus DNA ladder Control lane containing sample DNA at ---- (add size markers on right column) Absent genomic DNA Table 2. Measurement of the DNA concentration of the purified PCR reactions obtained from amplifying the TAS2R38 gene from student human genomic DNA. 2
purified TAS2R38 PCR1 purified TAS2R38 PCR2 DNA concentration (ng/ul) 3 7 Ratio 260/280 1.5