Slide 1 / 25 Slide 2 / 25 New Jersey Center for Teaching and Learning BIOLOGY Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of Population Genetics Lab students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning Evolution community, and/or provide access to course materials to parents, students and others. www.njctl.org Click to go to website: www.njctl.org http:/ / njc.tl/ 16 http:/ / njc.tl/ 6 Slide 3 / 25 Slide 4 / 25 Purpose Materials Students will investigate a genetically inherited trait and apply 1 strip of PTC Paper the Hardy-Weinberg Principle to a population. They will demonstrate the stability of allele frequencies over five 1 strip of Control Paper generations in an ideal Hardy-Weinberg population and they will then examine the effects of natural selection and 4 Index Cards heterozygous advantage on allele frequencies in a simulated mating exercise. 1 Coin Calculators Slide 5 / 25 Slide 6 / 25 Procedure A: Procedure A: Using the Hardy-Weinberg Principle to Calculate Allele Frequencies Using the Hardy-Weinberg Principle to Calculate Allele Frequencies You will test your ability to taste PTC (phenylthiocarbamide). The Step 3 Obtain the results for the entire class and enter the results ability to taste this bitter chemical is governed by a dominant allele. in Table 2. You will determine the allele frequencies for this trait in your class population. DO NOT share PTC and control strips with other Step 4 Using the Hardy-Weinberg equation, calculate the students. Use them once and dispose of them in the trash frequencies of each allele. You must show your work. when you are done. Step 1 Obtain a piece of PTC test paper and place it on your tongue. Notice if you can detect a bitter taste or not. If you can, you possess the trait to taste PTC. Record your results in Table 1. Step 2 Obtain a piece of control paper and place it on your tongue. Compare your results with the PTC paper to your results with the control paper to help you determine if you indeed can taste the PTC or not. Record your results in Table 1. Dispose of both test strips in the trash.
Slide 7 / 25 Slide 8 / 25 Data Procedure B: Testing the Hardy-Weinberg Principle: Case 1 An Ideal Population Taster Non Taster Your class will serve as the population for this and the following PTC exercises. Each index card represents a haploid chromosome. Each student will have two “A” cards and two “a” cards. Each Control parent will begin with the genotype Aa; therefore, initial genotype frequencies will be as follows: AA: 0.25 Aa: 0.50 Phenotypes Allele Frequency aa: 0.25 Tasters Non Tasters Record these initial frequencies under Case 1 below. p q # % # % Class Population Slide 9 / 25 Slide 10 / 25 Procedure B: Procedure B: Testing the Hardy-Weinberg Principle: Case 1 An Ideal Population Testing the Hardy-Weinberg Principle: Case 1 An Ideal Population Step 5 Depending on which genotype you are assuming, you may Step 1 Obtain four index cards. Label two cards with an “A” and have to obtain different cards. For example if the two offspring you the other two with an “a”. These will serve as your haploid produced in number 3 are AA and Aa, one partner begins the next chromosomes. Under Case 1, record “Aa” as your initial genotype. generation with 4 “A” cards and the other partner will retain 2 “A” and 2 “a” cards. Step 2 Find a random “mate”. You can pair off with anyone. Step 6 Randomly choose another classmate to pair off with for the Step 3 Turn you cards upside down and shuffle them. Turn over next generation and repeat steps 3 and 4. Each partner will record the top card in your pile. Your partner should do the same. These his or her genotype next to “F 2 Genotype” under Case 1. two cards will represent the genotype of your first offspring. Repeat this by each of you turning over a second card and pairing Step 7 Repeat steps 3 and 4 for three more generations for a total them. This will represent the genotype of your second offspring. of 5 generations. Step 4 Your partner and yourself will now assume the genotypes of Step 8 Tally the genotypes of the 5 th generation of the entire class the two offspring that you produced in number 3. One of you and record the results under Case 1. assumes the genotype of the first offspring and the second partner assumes the genotype of the second offspring. Each partner will Step 9 Calculate the frequency of “A” and of “a” after five record his or her genotype next to “F 1 Genotype” under Case 1. generations of random mating in your population. Slide 11 / 25 Slide 12 / 25 Data Data Final Class Frequencies: AA: _____ Aa: _____ aa: _____ Initial Class Frequencies: AA: _____ Aa: _____ aa: _____ p: ___ q: ____ Your Initial Genotype: _____ Number of “A” alleles present at the fifth generation Number of offspring with genotype AA ________ X 2 = __________ A alleles F 1 Genotype: _____ Number of offspring with genotype Aa_________ X 1 = __________ A alleles F 2 Genotype: _____ Total = _________ A alleles F 3 Genotype: _____ p = TOTAL number of A alleles TOTAL number of alleles in population = __________ F 4 Genotype: _____ Number of “a” alleles present at the fifth generation F 5 Genotype: _____ Number of offspring with genotype aa ________X2 = ___________ a alleles Number of offspring with genotype Aa _______X1 = ___________ a alleles Total = ___________a alleles q = TOTAL number of a alleles = _________ Total number of alleles in the population
Slide 13 / 25 Slide 14 / 25 Procedure B: Procedure B: Testing the Hardy-Weinberg Principle: Case 2 Selection Testing the Hardy-Weinberg Principle: Case 2 Selection Step 1 Follow the same procedure as in Case 1 except that if you In this exercise, we will be adding selection to make it a more realistic produce an offspring with the “aa” genotype, it does not survive; situation. In this case, there is 100% selection against homozygous therefore, you must eliminate these two alleles from the recessive offspring. The recessive allele in this case is mutated population. I order to maintain population size, you must produce making an “aa” individual non-viable. “Aa” and “AA” are viable and two surviving offspring. If you have to eliminate alleles due to the will be able to reproduce. You will need to have some extra index death of an offspring, you must draw two new alleles from the cards for this exercise since selection can lead to elimination of extra cards. (You can randomly write “A” or “a” on the extra certain alleles if an offspring dies due to being “aa”. cards). Step 2 Repeat the above procedure for a total of five generations, selecting against any “aa” offspring in each generation. Record the genotypes after each generation below. Step 3 Tally the genotypes of the 5 th generation of the entire class and record the results under below. Step 4 Calculate the frequency of “A” and of “a” after five generations of random mating in your population. Slide 15 / 25 Slide 16 / 25 Data Procedure B: Testing the Hardy-Weinberg Principle: Case 3 Heterozygous Advantage Initial Class Frequencies: AA: _____ Aa: _____ aa: _____ Your Initial Genotype: _____ Another type of selection is in certain diseases where a homozygous dominant individual is more severely affected than a heterozygote. F 1 Genotype: _____ One example is malaria. In this case, the heterozygote is favored over the homozygote dominant genotype and is selected. As in case F 2 Genotype: _____ 2, you will need extra cards for this exercise. F 3 Genotype: _____ F 4 Genotype: _____ F 5 Genotype: _____ Final Class Frequencies: AA: _____ Aa: _____ aa: _____ (After five generations) p: ___ q: ____ Slide 17 / 25 Slide 18 / 25 Data Procedure B: Testing the Hardy-Weinberg Principle: Case 3 Heterozygous Advantage Initial Class Frequencies: AA: _____ Aa: _____ aa: _____ Step 1 Follow the same procedure as in Case 2, eliminating any “aa” Your Initial Genotype: _____ individuals and their alleles. Additionally, if an “AA” offspring is produced, flip a coin. If the coin lands on “heads”, the offspring does F 1 Genotype: _____ not survive. If the coin lands on “tails”, the offspring lives. F 2 Genotype: _____ Step 2 Repeat the procedure for a total of five generations and record the genotypes of every generation below. F 3 Genotype: _____ Step 3 Calculate the frequency of “A” and of “a” after five generations F 4 Genotype: _____ of random mating in your population. F 5 Genotype: _____ Step 4 Continue the procedure for five more generations for a total of ten generations. Start with the genotypes from the end of the fifth Final Class Frequencies: AA: _____ Aa: _____ aa: _____ generation. Record your results below. (After five generations) p: ___ q: ____ Step 5 Calculate the allele frequencies after ten generations of random mating.
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