Gene Frequencies and the Hardy Weinberg Principle

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Abstract
The purpose of this experiment was to determine the correlation between the ability to taste the bitterness of phenylthiocarbamide, an organic compound used in genetics, and the ability and response of the tasting sodium benzoate paper, a food preservative. It is claimed that there is a direct relationship between the genes that control the tasting abilities of these two substances, primarily that if you had the ability to taste PTC, you would have a specific taste response for sodium benzoate, as well.

After the experiment results were analyzed, it was determined that there is no direct correlation between the ability to taste the substances. Non-tasters and tasters of phenylthiocarbamide had nearly the same reaction to sodium benzoate, disproving the claim that non-tasters will not experience a bitter response to sodium benzoate.

It was also determined that the Hardy-Weinberg Principle results are inaccurate due the the test strips in the experiment being of a low PTC concentration, and as many tasters of PTC can actually only respond to high levels of concentration, the recorded observations would be skewed.

Introduction
The purpose of this experiment was to determine if there is a testable relationship between the ability to taste phenylthiocarbamide and sodium benzoate. Phenylthiocarbamide, or PTC, is an organic compound useful for genetic experiment; sodium benzoate is commonly used as a food preservative. The ability to taste PTC and recognize it as having a bitter taste is a representation of the dominant gene - non-tasting is an example of the recessive. However, PTC is not always a one-way trait. Some tasters can only identify PTC at high-concentration levels, so they could be marked as a non-taster at a lower level of PTC concentration (CarolinaTM Taste Papers). This is what makes the phenylthiocarbamide gene so interesting: you can not identify one’s phenotype until they are specifically tested for the gene (Wooding, 2006). When tasting PTC paper, you either taste the bitterness and have the gene, or you don’t. When tasting the sodium benzoate, there is a much wider variety of the tastes you might experience (the most often are sour, sweet, salty, bitter, and no taste). It has been thought, and tested, that there is direct relationship between tasting PTC and sodium benzoate; for example, if you don’t possess the gene for tasting PTC, you will not observe a bitter taste from the sodium benzoate (Allaire, 2006).

The other purpose of this experiment was to determine if the Hardy-Weinberg Principle applies to the gene frequencies of the dominant and recessive alleles for the ability to taste phenylthiocarbamide. The Hardy-Weinberg Principle is a mathematical concept nearly necessary to population genetics. In order for the Principle to apply, however, the population must meet certain standards, including a large number of members, random mating, no mutations, no natural selection, no migration into or out of the population, and no genetic drift. The equation, p2 + 2pq + q2 = 1, allows scientists to calculate the allele frequencies in a population. The letter ‘p’ represents the frequency for the dominant allele (ability to taste PTC), ‘q’ represents the frequency of the recessive allele (unable to taste PTC), and ‘pq’ represents the heterozygous allele. However, the Hardy-Weinberg Principle fails more often than not due to the human population not meeting all of the necessary factors to reach the Hardy-Weinberg equilibrium (General Books LLC, 2010).

Materials
100 test subjects, ages 12-14
100 strips of phenylthiocarbamide (PTC) test paper
100 strips of sodium benzoate test paper
100 strips of white computer paper (control paper)
Pen or pencil
100 quizzes for test subjects to take, including questions asking gender, age, and the tastes that they observed for all three papers

Methods
In the experiment, students of the ages twelve to fourteen were tested for their ability to...
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