Text Readings in Lewis	Review questions
Chapter 18 Chapter 20	Pg. 388: To Review; 1, 2, 3, 5, 6, 7, 9, and 10 To Think About; 4 and 7 Pg. 420-1: To Review; 1, 3, 5, 6, and 7 To Think About; 3, 6 and 7

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Objectives
After studying this material you should be able to:

1. List and explain the factors that must be in play for a population to exprience NO change in allele frequencies over several generations (Hardy-Weinberg equilibrium).

2. Explain factors that increase genetic variation in a population.

3. Explain factors that decrease genetic variation in a population.

4. Describe an example of how genetic drift, a bottleneck event, or the founder effect could affect the genetic constitution of a population.

genetic drift	Hardy-Weinberg equilibrium	bottleneck
founder effect	gene flow	random mating
sexual reproduction	chance events	geographic isolation

Web Crossing Resources

Extra Credit Discussion - Book Reviews of The Beak of the Finch
Some of your classmates are reading, reviewing, and discussing this book dealing with natural selection and evolution.

Factors Affecting Genetic Variation in a Population
Biodiversity & Evolution Model

• No change in allele frequencies (genetic variation maintained) = No Evolution: Hardy-Weinberg Equilibrium
  • An idealized state in which the proportion of genotypes in a population remains constant over many generations.

  • Requires:
    • random mating
    • large population
    • no migration
    • no mutation
    • no natural selection

• Factors that Increase Genetic Variation
  • Sexual Reproduction (mixing of existing alleles)
    • Meiosis (independent assortment and crossing over)
    • Fertilization

  • Mutation (creation of new alleles)

  • Gene Flow - Increased variation due to migration INTO a population

• Factors that Decrease Genetic Variation
  • Natural Selection- favors some phenotypes and the alleles that produce them and removes others from the population.

  • Genetic Drift
    • Changes in allele frequencies due to random, chance events

    • Happens in both large and small populations, but the effects in small populations are greater than those in large populations (Florida panther as road kill)

    • NOT a form of selection, but may work in conjunction with selection

  • Bottleneck - A rapid, drastic reduction in the size of a population that may result in genetic drift (Cheetahs, Fig. 20.5, p. 409 & Mt. Toba and Human evolution)

  • Founder Effect - The establishment of a new, geographically isolated population that may result in genetic drift.

  • Gene Flow - loss of variation due to migration OUT of a population