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2 Chapter16 2 Chapter16 Presentation Transcript

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