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The Forces of Evolutionary Change--Microevolution

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15.1 Evolution is Highly Probable

1. A gene pool includes all the genes in a population. Allele movement between populations is gene flow. Inherited characteristics of the individuals in a population reflect allele frequencies.  
2. In Hardy-Weinberg equilibrium, evolution is not occurring because allele frequencies do not change from generation to generation. In this idealized state, we can calculate the proportion of genotypes and phenotypes in a population by inserting known allele frequencies into an algebraic equation: p2 + 2pq + q2. The equation also can reveal allele frequency changes when we know the proportion of genotypes in a population. Animation
Hardy-Weinberg Equilibrium

Essential Study Partner
Conditions that Cause Evolution

Essential Study Partner
Natural Selection

Essential Study Partner

Art Quiz
Hardy-Weinberg Equilibrium

15.2 Mate Choice and Evolution

3. When allele frequencies change, evolution occurs.  
4. Nonrandom mating causes certain alleles to predominate because a particular phenotype is more attractive to the opposite sex.  
5. In genetic drift, small populations separate from larger ancestral populations and establish a new gene pool, with different allele frequencies. The founder effect and population bottlenecks are forms of genetic drift.  

15.3 Mutation Fuels Evolution

6. The deleterious alleles in a population constitute its genetic load.  
7. Mutation alters allele frequencies by changing one allele into another and providing new phenotypes for evolution to act on. Exploration
8. Harmful recessive alleles are selected against in homozygotes, but heterozygotes maintain them and mutation introduces them into the gene pool. Art Quiz
Sickle Cell Allele and Malaria

15.4 Natural Selection Molds Evolution

9. In directional selection, an extreme phenotype becomes more prevalent in a population. Industrial melanism is an example.  
10. In disruptive selection, extreme expressions survive at the expense of intermediate forms.  
11. In stabilizing selection, an intermediate phenotype has an advantage. Essential Study Partner
Types of Selection

Art Quiz
Types of Natural Selection
12. Balanced polymorphism is a form of stabilizing selection that maintains deleterious recessive alleles because heterozygotes are protected against another medical condition.  

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