PTC! How Many Guys and Gals in My Class can Taste PTC? Are there Gender Differences?

Research Questions:

• What is the Hardy-Weinberg principle of equilibrium? 
• What are alleles? 
• How does the Hardy-Weinberg principle assist us in making predictions in the field of genetics?

On the information level, this experiment serves to acquaint students with basic information on the Hardy- Weinberg Principle of equilibrium which tells us that the genetic variation in a population will remain constant from one generation to the next provided there are no disturbing factors. Disturbing factors will include mutations, natural selection, non random mating, genetic drift and gene flow. When mating is random in a large population with no disruptive circumstances, the principle predicts that both genotype and allele frequencies will be constant due to the fact that they are in equilibrium. However, given the fact that in real life there are many disruptive variables, the Hardy Weinberg equilibrium is not maintained. Genetic equilibrium serves as a base from which we may measure genetic variations. In this project, the ability to taste PTC serves as an example that disturbing influences are always present. Using the Hardy-Weinberg principle we are able to determine useful but difficult to measure facts about the population. This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control when required, of identifying dependent and independent variables, of selecting a large enough sample of subjects when applicable to the objective, of accurate and organized data collection, of pictorial and or graphic presentation of data and of being able to m ake better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as scientist.

Materials:

• PTC (phenylthiocarbamide) taste test strips (100 in a vial)
• control paper strips
• mints
• paper cups
• water
• The PTC taste test strips and the control strips may be obtained from Chem. Scientific or Carolina Biological.

Experimental Procedure:

1. Gather all the materials you will need to conduct your experiment. These include the PTC taste test strips, the control strips consisting of just plain look alike strips with no PTC, blind folds, paper cops, water and mints. Keep the PTC strips out otof the sun.
2. Copy the data chart provided on the next page to record your data.
3. Make certain that you have a sufficient number of classmates and an equal distribution of boys and girls. Set up a control group and an experimental group each with an equal number of boys and girls. Do not inform the subjects as to which group they have been placed.
4. Design and reproduce a response card for each subject on which they are to check their reaction to the taste strip, no taste, a slight bitter taste or a revolting taste.
5. For each subject, depending on the group in which they have been placed, provide a strip, be it the real PTC or the control. Have them place the strip on the tongue and then record on the card whether there was no taste, a slight bitter taste or a revolting taste. Provide cups of water for rinsing the mouth and mints for those who require them.
6. You may wish to take photos of the experiment to display at the Science Fair and to include in your final report.
7. Collect all your response cards and record the data. Analyze the data and summarize the results. Write up your report. Make certain to include all of your research as well as your bibliography. You may wish to include your reactions to conducting this experiment. Was it of any value? How did you profit from this project?

                                                                                  Chart #1: PTC Tasters

Chart #2: Control Data

Terms/Concepts: Genes, alleles, Hardy-Weinberg equilibrium, natural selection, mutations, genetic drift, PTC, genetic variation

References:

Wikipedia Encyclopedia, search on PTC Modern Biology, Holt, Rinehart and Winston Orlando Florida 1991