Genetics of Taste Perception – Lab Activity
Today’s F2F lab will investigate the genetic determinants of taste perception. The broad question framing today’s activity is the following: To what degree does our genetic makeup influence our food preferences?
Part I. To start, take a moment to think about your favorite and least favorite foods. Share your preferences within your lab group – are there any similarities?
Next, fill out the short veggie survey below. If you haven’t tried one of the vegetables, just mark the ‘don’t know’ box.
Vegetable I like this one!
I don’t mind eating it
I avoid it, if possible
It’s awful, I never eat it
Don’t know
Alfalfa sprouts Arugula Beet Bitter melon Bok choy Broccoli Brussels sprouts Cabbage Carrot Cauliflower Celery Chard Chinese Broccoli Cilantro Collards Daikon Dandelion greens Eggplant Endive Horseradish Jalapeno Kale Kohlrabi Mustard greens Nutmeg Potato Radicchio Red radish Rutabaga Spinach Tomato Turnip Watercress
Part II. For the second section of this lab, you and your fellow lab members will collect some data to characterize phenotypic variation in bitter taste perception within your class population.
Remember from the lab background reading that there are at least 30 different types of bitter taste receptors in humans: since many of the genes coding for these receptors come in several forms (alleles), there should be some natural variation in individuals’ perception of bitter taste.
The best-‐studied bitter taste receptor gene, TAS2R38, is involved in the ability to taste (or not taste) the chemical PTC. Humans also vary in their perception of the common food preservative, sodium benzoate. Your lab instructor will pass out three different individual paper test strips:
1. PTC test paper strip 2. Sodium benzoate test paper strip 3. Plain filter paper strip
There will also be a jug of water and cups available – pour yourself a cup of water and take one of each type of paper, making sure to maintain the identity of type of paper.
Procedure: (as you work through this procedure, you can record your results at the bottom of this page)
1. Rinse your mouth with water to clear your palate 2. Taste the plain filter paper and note any flavor – this is your baseline or control (since
the two chemicals you’ll be tasting are delivered on filter paper). Note whether the filter paper alone has no taste, or if you can detect any bitterness.
3. Rinse your mouth with water 4. Taste the sodium benzoate paper and record whether you perceive bitter, salty and/or
sweet (taster). You may also taste nothing (nontaster). Record whether you are a taster or nontaster; if you are a taster describe the flavor. Keep in mind that you may taste one or all three of the sensations.
5. Rinse your mouth with water 6. Taste the PTC paper and record your taste perception as very bitter, mildly bitter, or no
taste. 7. Record your results on the class data sheet on the front board
Data Analysis: Once you have completed Parts I and II, begin answering the questions on pages 3-‐4. Your completed answers to the questions are due turned in to your lab instructor by the end of today’s F2F lab.
Results:
Filter paper: _________________
Sodium Benzoate: Taster:_____ Non-‐Taster:_____
If Taster, do you taste: Sweet?___ Salty?___ Bitter?____
PTC: Very Bitter ____ Mildly Bitter ____ No Taste ____
Name:__________________________________
Genetics of Taste Perception: Questions
1. Sodium benzoate perception: What percentage of your classmates is considered a
a. Taster?
b. Nontaster?
Of those tasters, how many perceived the paper to be
a. salty?
b. sweet?
c. bitter?
2. PTC perception: What percentage of your class is considered a
a. Taster?
b. Mild taster?
c. Nontaster?
3. What are the possible genotypes of the classmates who can taste PTC (either strongly or mildly)?
4. What is the genotype of the classmates who are PTC non-‐tasters?
5. How many students who tasted PTC also perceived sodium benzoate as bitter?
6. Do you think the same chemoreceptor that recognizes and binds to the chemical PTC can recognize and bind to sodium benzoate? Why or why not?
7. From an evolutionary perspective, why do you think there is so much variation in the human population for detecting bitter tastants as compared to sweet, sour, or umami?
8. Do an informal poll of your classmates (your lab instructor may wish to create a new table on the board for this purpose). Which vegetables from the food preferences survey on page 1 did students who are PTC tasters dislike the most? Which vegetables did non-‐tasters dislike the most?
Are there any differences in food preferences between tasters and non-‐tasters? Explain your findings in terms of the relative contributions of genetic and environmental influences on phenotype.
