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Candace Berkeley
Product Developer
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The Hardy-Weinberg principle states that allele and genotype frequencies remain stable in a population over generations if certain conditions are met:
When all of these conditions are met, the population is said to be in Hardy-Weinberg equilibrium. If the allele or genotype frequencies do change over time, then scientists assume that 1 or more of the conditions is not being met and the population may be evolving.
The Hardy-Weinberg equation allows scientists to estimate the allele and genotype frequencies in a population. The frequencies can be compared across generations to determine whether evolution may be occurring. Assuming that a population includes only 2 alleles for a given trait, the proportion of dominant alleles (p) plus the proportion of recessive alleles (q) is equal to 1 (i.e., 100% of the population). Squaring both sides of the equation p + q = 1 produces the equation p2 + 2pq + q2 = 1. Here p2 is the number of individuals with a homozygous dominant genotype, 2pq is the number of individuals with a heterozygous genotype, and q2 is the number of individuals with a homozygous recessive genotype.
The Hardy-Weinberg principle is often hard for students to understand. Evolution is difficult to observe in nature, but modeling an evolving population of edible treats effectively engages your students in the Hardy-Weinberg principle and demonstrates what happens when Hardy-Weinberg conditions are not met. The following 2 activities generally take no more than 30 min of class time. Class data will likely indicate stable genotype frequencies in Activity 1 but varying frequencies in Activity 2.
Once class data are collected, have students compare the genotype frequencies in both simulations. The class data from the first activity should result in fairly constant frequencies over the 5 generations. When selection is introduced in the second activity, the genotype frequencies should vary over the 5 generations. Discuss what conditions must exist for frequencies to remain stable over multiple generations. What do changing frequencies indicate in a population? Have students discuss whether Hardy-Weinberg equilibrium is possible in nature.