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Overview: This hands-on activity, used in conjunction with a short film, teaches students about population genetics, the Hardy-Weinberg principle, and how natural selection alters the frequency distribution of heritable traits. It Author/Source: Howard Hughes Medical Institute Grade level: 13-16 Time: 2-3 50 minute class periods Teaching tips: To do the activity in only two class periods, you can assign one section of the activity as homework. However, nswers to the worksheet are readily available online, so if this is a concern, you may wish to do the activity in class. Concepts: Correspondence to the Next Generation Science Standards is indicated in parentheses after each relevant concept. See our conceptual framework for details. There is a fit between organisms and their environments, though not always a perfect fit. Evolution is often defined as a change in allele frequencies within a population. The Hardy-Weinberg equation describes expectations about the gene pool of a population that is not evolving—one that is very large, mates randomly, and does not experience mutation, natural selection, or gene flow. Evolution results from natural selection acting upon genetic variation within a population. Natural selection and genetic drift act on the variation that exists in a population. Natural selection acts on phenotype as an expression of genotype. Inherited characteristics affect the likelihood of an organism's survival and reproduction. Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing. Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental. Natural selection can act on the variation in a population in different ways. Natural selection sometimes favors heterozygotes over homozygotes at a locus. As with other scientific disciplines, evolutionary biology has applications that factor into everyday life, for example in agriculture, biodiversity and conservation biology, and medicine and health. Teacher background: Genetic Variation Natural Selection

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