Introduction:

Testing the ability to taste phenylthiocarbamide (PTC) has been linked to many things, one of which is evolution. The ability to taste PTC is inherited. Tasting PTC is a dominant trait and the recessive allele is for non-tasting. However, PTC tasting is not an “either/or” trait. There is great variability in the ability to taste. Students who have two copies of the dominant allele will find that PTC Taste Paper is extremely bitter. Students with only one dominant allele will report a bitter taste, but will not react as strongly as people with two dominant alleles. Students with two recessive alleles will not be able to taste the PTC on the paper and are considered non-tasters.

PTC is associated with bitter taste and is compound widely found in broccoli, cauliflower, and other members of the mustard family. Food preference studies show that PTC tasters tend to avoid these vegetables and other strongly flavored foods. Non-tasters tend to eat a more varied diet that includes green leafy vegetables. Others have pointed out that plant poisons are often bitter; thus, the ability to taste bitter substances might be important in hunter-gatherer societies.

All three genotypes (extreme tasters, tasters, and non-tasters) are found in Europe. The recessive trait is uncommon in Asia, and Native Americans carry the dominant allele almost exclusively. The greatest variation in PTC alleles is found in African populations. **This is consistent with the idea that founding populations moved out of Africa into Europe and Asia, and later moved from Asia to the Americas.

Goal: Test all classmates with control paper and PTC paper and record the data on a table. Also record their preferences for food on a data table.

Part 1: Review

1.  List the phenotypes and genotypes that match the characteristics:

Phenotype (trait) / Genotype (alleles/letters) / Characteristic / Where the trait is common
Can taste the PTC very strongly
Can taste the PTC
Cannot taste PTC

2.  What is PTC associated with?

3.  If you can taste PTC, what foods will you avoid?


Part 3: Study the students in your class

Directions:

A.  Get the name of each student and write it in the data table.

B.  Give student a control paper to taste first. Throw it away.

C.  Give student the PTC paper to taste. If student can taste the bitter flavor, mark them as “TASTER” on the table. If the student cannot taste PTC, mark them as “NON-TASTER” on the table. Throw it away.

D.  Ask student supplemental questions to fill into data chart.

Data Table 1:

Student Name / Taster / Non-Taster / Ethnicity? / Likes Broccoli?
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.

Part 4: Analyze the results

1.  Could you taste the PTC?

2.  Which genotype and phenotype do you have?

3.  How many students were non-tasters and tasters?

4.  What percentage were non-tasters and tasters? (You have to cross multiply & solve for x)

# of non-tasters or tasterstotal number of students tested= x100

5.  How can being a taster be an advantage?

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