Featured in PASCO’s Advanced Biology through Inquiry Teacher Guide
This manual features 22 challenging, standards-based, inquiry lab activities for AP, IB, and honors programs.
Students determine their phenotype for the PTC (phenylthiocarbamide) tasting trait and use class data to derive allele frequencies for a population.
Students use class data for the PTC (phenylthiocarbamide) tasting trait to derive allele frequencies for a population. Based on their phenotype and predicted genotype, students use “allele cards” to simulate the next generation and determine if allele frequencies change over time in the absence of selection, non-random mating, mutations, and migration. Students may or may not observe genetic drift in the simulation due to the small population size of the class. Student-designed experiments focus on determining the effect of violating one of the Hardy–Weinberg conditions on allele frequencies in a gene pool.
The Initial Investigation is a teacher-directed activity. Be sure to review the directions of the investigation carefully so you are prepared to guide students through the steps and calculations. Prior to the investigation, determine how you would like students to report their PTC phenotypes. Depending on class size, you may wish to just verbally poll the class. Alternatively, you can create a chart on the front board and ask students to come to the front and record a tally mark in the correct column. Another option is for a group leader to go to the front board to report the phenotypes for all members of that group. Before directing students to acquire allele cards from the gene pool, you will need to assign some of the tasters to be homozygous in genotype (TT) and others to be heterozygous (Tt). For example, if you have 18 students who are tasters and five of these should be of the homozygous genotype, you can ask all tasters to raise their hands and then point to five students who have their hands raised and ask that they be homozygous. You may need to help the class determine the total number of T and t alleles in the gene pool, which students are directed to do in the Initial Investigation. Each homozygous dominant individual has 2 T's, so the number of T alleles for this genotype is 2 × number of persons of that genotype. Each heterozygote has 1 T and 1 t, so the T alleles and t alleles for this genotype are equal to the number of individuals with the genotype. Lastly, the number of t alleles from the homozygous recessive individuals is 2 × the number of person of that genotype.
This experiment may require software and an interface for data collection.