• [Mechanisms of evolution: Grades 9-12] Evolution results from selection acting upon genetic variation within a population. (LS4.B)
• [Mechanisms of evolution: Grades 9-12] There is variation within a population. (LS3.B)
• [Mechanisms of evolution: Grades 9-12] Natural selection acts on the variation that exists in a population. (LS4.B, LS4.C)
• [Mechanisms of evolution: Grades 9-12] Natural selection acts on phenotype as an expression of genotype.
• [Mechanisms of evolution: Grades 9-12] The amount of genetic variation in a population may affect the chances of survival of the population; the less diversity, the less likely the population will be able to survive environmental change.
• [Mechanisms of evolution: Grades 9-12] Over time, the proportion of individuals with advantageous characteristics may increase due to their likelihood of surviving and reproducing. (LS4.B, LS4.C)
• [Mechanisms of evolution: Grades 9-12] Fitness is reproductive success — the number of viable offspring produced by an individual in comparison to other individuals in a population/species.
• [Mechanisms of evolution: Grades 13-16] Evolution results from natural selection acting upon genetic variation within a population.
• [Mechanisms of evolution: Grades 13-16] Natural selection and genetic drift act on the variation that exists in a population.
• [Mechanisms of evolution: Grades 13-16] Natural selection acts on phenotype as an expression of genotype.
• [Mechanisms of evolution: Grades 13-16] Over time, the proportion of individuals with advantageous traits may increase (and the proportion with disadvantageous traits may decrease) due to their chances of surviving and reproducing.
• [Mechanisms of evolution: Grades 13-16] Natural selection sometimes favors heterozygotes over homozygotes at a locus.
• [Mechanisms of evolution: Grades 13-16] Heterozygote advantage preserves genetic variation at that locus (i.e., within the population, it maintains multiple alleles at that locus).
• [Mechanisms of evolution: Grades 13-16] An individual's fitness (or relative fitness) is the contribution that individual makes to the gene pool of the next generation relative to other individuals in the population.
• [Mechanisms of evolution: Grades 13-16] An organism's fitness depends on both its survival and its reproduction.
• [Studying evolution: Grades 9-12] As with other scientific disciplines, evolutionary biology has applications that factor into everyday life.
• [Studying evolution: Grades 13-16] 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.

• Disciplinary Core Idea LS3.B: Variation of Traits
• Disciplinary Core Idea LS4.B: Natural Selection
• Disciplinary Core Idea LS4.C: Adaptation

This article encourages students to reason about scientific data. It includes a set of discussion and extension questions for use in class, as well as hints about related lessons that might be used in conjunction with this one. Get more tips for using Evo in the News articles in your classroom.

Additional teaching tips for 13-16:
Use this resource to relate evolutionary concepts to the topics of Mendelian genetics and conservation (or get more suggestions for incorporating evolution throughout your biology syllabus). This story provides an excellent example of harmful recessive alleles and inbreeding depression in context.

• Genetic Variation