Investigation I: PTC Lab

 Investigation I: PTC Lab

Hypothesis: If the allele for tasting PTC is dominant then more people will be able to taste PTC.

Materials: 

• Control Strip 
• PTC Taste Strip
• Sample Population Like a Classroom
• Notebook and Writing Utensil
• Data Table

Procedure:

1. Students groups should obtain a PTC taste strip and a control strip.
2. Every member of the group should first taste the control strip of paper.
3. Every person should taste the PTC impregnated strip of paper. Compare the taste of the control and the PTC paper.  If you are a taster, the PTC paper strip will be bitter. Non-tasters will not notice a difference between either strip of paper.
4. For the class, record the total number of tasters and the total number of non-tasters on the blackboard. Also record the results in your lab notebook.
5. Determine decimal value by division for tasters (p2 + 2pq), and likewise the decimal value for non-tasters (q2).
1. For example, there are 100 people in your class. 25 are non-tasters and 75 are tasters.
2. Then 25/100, or 0.25, is the frequency of non-tasters, and 75/100, or 0.75, is the frequency of tasters.
6. Record your values in Table 1. Use Hardy-Weinberg as described above to determine the value of p and q for your class.

Table 1: Phenotypes and Gene Frequencies for Trait to Taste PTC

Table 1;  Phenotypes and Gene Frequencies for Trait to Taste PTC
		Class Phenotypes		Allele Frequency Calculated by the Hardy Weinberg Equation
		%Tasters	% non-tasters	p	q
		P2 +2pq	q2
Class Population		0.76 = 76%	0.24 = 24%	0.51	0.49
North American Population		.55	.45	0.33	0.67

Questions: 

1. What is the frequency of homozygous tasters , P2, in your classroom?
The frequency for homozygous tasters in the classroom is 0.26. You get this frequency by squaring the frequency for the dominant allele, 0.51.
2. What is the frequency of heterozygous tasters, 2pq, in your classroom?
The frequency of the heterozygous tasters in the classroom is 0.50. You get this by multiplying the frequencies for the dominant allele, the recessive allele and the number 2 together.
3. What is the frequency of homozygous non-tasters, q2,  in your classroom?
The frequency of the homozygous non-tasters in the classroom is 0.24. You get this frequency by squaring the frequency for the recessive allele, 0.49.
Determine the percentage of the three genotypes TT, Tt, and tt in your classroom.
TT = 26%
Tt = 50%
tt = 24%

Conclusion: 

The frequency for those who can taste PTC is higher than the frequency than those who can't taste PTC. In a classroom of 46 students, 76% of the students were able to taste the chemical while 24% of the students weren't able to taste it. This could be due to the higher allele frequency of the dominant allele which was 0.51. Even though the North American Population has a lower allele frequency for the dominant allele, 0.33, more people, about 55%, had the trait for tasting PTC. Therefore, my hypothesis, which stated that more people would be able to taste PTC, was correct. Any errors in this experiment could have been in the calculations of the gene frequencies. Possible changes to this experiment could be experimenting with a different group of people instead of a classroom.