Episode FourObservable Traits

Lesson Goal Gather data on an observable trait of you and your classmates; develop hypotheses (testable ideas) about what data you will see/hear.


Step One – Brush up on Basic Genetics

  • Review the following basics of genetics
  • Animals typically have two parts of every gene (sometimes things go wrong).
  • Each part is called an allele.
  • You get one allele from your biological mother, and one from your biological father.
  • Your genotype is the “type-o-gene” that you have (made up of alleles).
  • Your phenotype is what we see – the physical presentation and appearance (even if we have to look really, really closely to see it).
  • Sometimes an allele is dominant. Sometimes an allele is recessive.
  • If a dominant allele is paired with a recessive allele, generally the dominant gene is expressed
  • Generally, the only way to see a recessive trait is if both alleles are recessive alleles.

Step Two – Develop your Hypothesis

  • Define the Problem: The ability to taste PTC is a dominant trait. Will that dominant trait be observed more frequently than the recessive trait (inability to taste PTC)?
  • Answer the Question: Is the ability to taste PTC more common than not being able to taste it?
  • Choose your Hypothesis: (our testable idea)
    • There will be more students who can taste PTC, than students who cannot.
    • There will be more students who cannot taste PTC, than students who can.

Step Three – Run your Experiment

  • Clean your hands with the hand wipe provided by your teacher.
  • Place the entire strip of PTC-saturated paper in your mouth. Wait 5-10 seconds… then carefully spit the paper into the tissue provided for you.
  • Use the mint/hard candy if the PTC taste is really horrible. Never taste any substance in a lab unless directed to by your teacher!
  • Make a note on Data Table 1 whether or not you tasted the PTC (trust me, you’ll know!)
  • Count the number of students in your class who have the dominant trait (can taste PTC).
  • Count the number of students in your class who cannot taste the PTC (recessive trait).
  • Did anyone have an EXTREME reaction? These folks are the supertasters.
  • Add these results to Data Table 1
  • Complete the ratio and proportion section of your worksheet
  • Complete the graphing section of your worksheet
  • Think & Write about this:

    Do your findings support or refute your hypothesis?

    Do you think your findings are accurate? Why/Why not?

    If you were going to run this experiment again, what would you do differently, and why?


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