Peppered Moth Model

 The purpose of the peppered moth activity is to model the effects of natural selection on the appearance and genetic make-up of a natural population. By adjusting the amount of pollution in the environment, the student is able to see the differences in the frequencies of light and dark moths in the population. The student may also investigate the survival differences between dominant and recessive genes when one phenotype has a selective advantage over the other.

 TEACHER RESOURCES Teacher Materials Student Activity Student   Assessment Learning   Goals/Standards COMPUTER MODELS Based on a model from the Global Change program at the University of Michigan STELLA Versions isee Player software Right-click to download the models Vensim Versions Vensim PLE Software Right-click to download the model Web-based Simulation THE MODEL DIAGRAM THE EQUATIONS
 AA_mothies(t) = AA_mothies(t - dt) + (birth_1 - death_1) * dt INIT AA_mothies = 250 Aa_mothlets(t) = Aa_mothlets(t - dt) + (birth_2 - death_2) * dt INIT Aa_mothlets = 500 aa_moths(t) = aa_moths(t - dt) + (birth_3 - death_3) * dt INIT aa_moths = 250 birth_1 = (repro_rate * total_moths) * (big_A_allele ^ 2) death_1 = AA_mothies * (natural_mortality + bird_predation_dark) birth_2 = (repro_rate * total_moths) * (2 * big_A_allele * little_a_allele) death_2 = Aa_mothlets * (natural_mortality + bird_predation_dark) birth_3 = (repro_rate * total_moths) * (little_a_allele ^ 2) death_3 = aa_moths * (natural_mortality + bird_pred_light) AA_mothies_freq = AA_mothies / total_moths Aa_mothlets_freq = Aa_mothlets / total_moths aa_moths_freq = aa_moths / total_moths big_A_allele = ((2 * AA_mothies) + Aa_mothlets) / (2 * total_moths) bird_predation_dark = bird_pred_rate - (pollution * bird_pred_rate) bird_pred_light = pollution * bird_pred_rate bird_pred_rate = .04 dark_freq = (AA_mothies + Aa_mothlets) / total_moths light_freq = aa_moths / total_moths little_a_allele = ((2 * aa_moths) + Aa_mothlets) / (2 * total_moths) natural_mortality = .045 pollution = 0 repro_rate = .055 total_moths = AA_mothies + Aa_mothlets + aa_moths
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