2 Chapter16

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2 Chapter16

  1. 1. Chapter 16 Evolution of Populations Gene Pools are a common group of genes combined from the members of a specific population. In a gene pool, there is usually two or more alleles. An allele is a form of a certain gene. The number of times that an allele occurs in a gene pool compare with the number of times that another allele occurs is the relative frequency. Genes and Variation Kana and Sharrie :)
  2. 2. Sources of Genetic Variation <ul><li>Two main sources of genetic variation: </li></ul><ul><li>Mutations - any change in a sequence of DNA </li></ul><ul><li>Genetic Shuffling - different combinations of genes </li></ul><ul><li>These result from sexual reproduction. </li></ul>Kana and Sharrie :)
  3. 3. Single-Gene and Polygenic Traits <ul><li>Depending on how many genes control a trait, the number of phenotypes produced vary. </li></ul><ul><li>Single-gene trait: single gene controlled by two alleles </li></ul><ul><li>Polygenic trait: traits controlled by two or more genes </li></ul>Kana and Sharrie :)
  4. 4. Natural Selection on Single-Gene Traits <ul><li>Changes in allele frequencies which are caused by natural selection on single-gene traits lead to evolution. </li></ul>Kana and Sharrie :)
  5. 5. Natural Selection on Polygenic Traits <ul><li>There are three ways that natural selection can affect the distribution of phenotype types: </li></ul><ul><li>Directional Selection </li></ul><ul><li>Stabilizing Selection </li></ul><ul><li>Disruptive Selection </li></ul>Kana and Sharrie :)
  6. 6. Genetic Drift <ul><li>Genetic drift is a random change in allele frequency. </li></ul>Kana and Sharrie :)
  7. 7. Evolution versus Genetic Equilibrium <ul><li>The Hardy-Weinberg principle - </li></ul><ul><li>Allele frequencies will remain constant in a population unless changes occur. </li></ul><ul><li>For genetic equilibrium to occur, there must be: </li></ul><ul><li>Random mating </li></ul><ul><li>A large population </li></ul><ul><li>No movement into or out of the population </li></ul><ul><li>No mutation </li></ul><ul><li>No natural selection </li></ul>Kana and Sharrie :)
  8. 8. Isolating Mechanisms <ul><li>While new species evolve, populations become reproductively isolated. </li></ul><ul><li>Reproductive isolation - when the members of two populations cannot reproduce and make fertile offspring </li></ul><ul><li>There are three types of isolation: </li></ul><ul><li>Behavioral isolation </li></ul><ul><li>Geographic isolation </li></ul><ul><li>Temporal isolation </li></ul>Kana and Sharrie :)
  9. 9. SO BASICALLY… <ul><li>Speciation occurs by the founding of a new population, geographic isolation, changes in the new population’s gene pool, reproductive isolation, and ecological competition. </li></ul>Kana and Sharrie :)

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