Population Genetics and Hardy-Weinberg Populations Lab General ...

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q 2 + 2pq + p 2 = 1 Equation 1 For a gene with simple dominant/recessive inheritance, where q is the dominant allele you get the following. q 2 + 2pq = frequency of dominant phenotype Equation 2 p 2 = frequency of recessive phenotype Equation 3 It should be apparent from these equations that 2pq represents the frequency of the heterozygote while q 2 and p 2 represent the homozygotes. The equations can be drawn out to include even more alleles, but quickly become mathematically tedious. Testing a Random Population We can learn to work with the basic mathematics of Hardy-Weinberg and analyze some real data with a very simple experiment on the class. We will test whether the class population is in agreement with the population average distribution for a specific genetic trait. For this to work we need a trait that easily measured, demonstrates simple dominant/recessive inheritance, and is non-apparent in the overall population (so as to limit bias). The trait will use is the ability to test the chemical phenylthiocarbamide (PTC). Being able to taste the compound is a dominant trait in humans and allows you to detect a very bitter taste from this compound (don’t ask me to describe it any better, since I cannot taste it). Nontasters possess the recessive phenotype. Question 1 If you use “A” and “a” to designate the alleles for tasting and nontasting, what would the genotype(s) of a taster and nontaster be? Procedure 1. Take a piece of the PTC test paper and place it on your tongue. 2. Record whether you are a taster or nontaster on the lab data sheet. 3. Determine the percentage of the population that are tasters and nontasters from pooled lab numbers. 4. Since nontasters are homozygote recessives, the allele frequency for the recessive gene can be determined by taking the square root of the decimal percentage for nontasters (p 2 in equation 3). 5. The total distribution of alleles is p+q = 1, therefore the allele frequency for q (dominant allele) can be calculated. 6. Determining the frequency of homozygous dominant individuals is determined by squaring q. 7. The frequency of heterozygotes is determined by 2pq.
8. Record your results in provided table on the lab data sheet. 9. Compare to the provided values for North American populations. Question 2 What factors could play into our sample being different from the North American average. An Ideal Population In this experiment the entire class will represent an entire breeding population. In order to ensure random mating, choose another student at random. The class will simulate a population of randomly mating heterozygous individuals with an initial gene frequency of .5 for the dominant allele A and the recessive allele a and genotype frequencies of .25AA, .50 Aa and .25 aa. Your initial genotype is Aa. Record this in your notebook. Each member of the class will receive four cards. Two cards have a and two cards have A. The four cards represent the products of meiosis. Each “parent” contributes a haploid set of chromosomes to the next generation. Procedure 1. Begin the experiment by turning over the four cards so the letters are not showing, shuffle them, and take the card on top to contribute to the production of the first offspring. Your partner should do the same. 2. Put the two cards together. The two cards represent the alleles of the first offspring. One of you should record the genotype of this offspring in your notebook. 3. Each student pair must produce two offspring, so all four cards must be reshuffled and the process repeated to produce a second offspring. Then, the other partner should record the genotype. The very short reproductive career of this generation is over. 4. Now you and your partner need to assume the genotypes of the two new offspring. 5. Next, the students should obtain the cards requires to assume their new genotype. 6. Each person should then randomly pick out another person to mate with in order to produce the offspring of the next generation. Follow the same mating methods used to produce offspring of the first generation.
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Page 5 and 6: We will be starting with initial po

Population Genetics and Hardy-Weinberg Populations Lab General ...

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