This activity examines readily detectable traits in humans: the variation in the ability to taste the chemical phenylthiocarbamide (PTC) and to exhibit tongue rolling.

Using self generated data and related questions, students will explore Mendel's principles of inheritance and variation within populations. PTC testing facilitates discussion about the phenotypic differences due to the single nucleotide polymorphisms (SNPs). Students will review Mendelian inheritance, genetic variation such as SNPs and other gene mutations and human pedigrees. Student PTC data is used for a population genetics exercise using the Hardy-Weinberg Model.


  • To develop a better understanding of the relationship between genotype and phenotype;
  • To draw conclusions from a data set they helped create.

Context and requirements

Level College
Discipline Biology
Course General biology 1
Activity Content The genetics of PTC sensitivity and tongue rolling
Technological Requirements Clickers/clicker pads
Best Use Case study for 1-2 class sessions

Author’s Notes


  • The exercise involves personal and memorable example of Mendelian inheritance and the Hardy-Weinberg model;
  • PTC testing highlights how people can experience the same stimulus differently.


  • Given the nature of the activity keeping students on task and answering questions can be challenging;
  • Students sometimes falsely report results of the PTC strips (false positives).


  • Give each student one PTC and one control test strips, omit data from students who can taste both strips.

Activity Pedagogical Components


For a description of this strategy, please see here.


For a description of this strategy, please see here.

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