Claudograms

• I CAN discuss


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• Dad Joke: 'I'm reading a book on evolution... The beginning wasn't great, but it's getting better over time.'
• Carl Sagan - Cosmos, 1980: 'The environment selects those few mutations that enhance survival, resulting in a series of slow transformations of one life form into another, the origin of a new species.'
• We think that evolution always progresses toward "better species".
• Although evolution through natural selection results in species with traits that are better adapted to survival, this does not mean that evolution is progressive.
• Even through natural selection, organisms have a variety of traits that are not perfectly suited to survival.
• In addition to natural selection, other mechanisms of evolution do not result in adaptive change, such as migration and genetic drift.
• One common misconception is that individual organisms evolve
• Natural selection acts on individuals, but only populations can evolve
• For example, mean beak size evolved in a population of medium ground finches on Daphne Major Island
• Looking at the graph average beak depth increased in the finch population because birds with smaller beaks were less likely to survive and reproduce
• The finch population evolved, NOT its individual members
• Evolution


  (in a biological sense) change in the genetic makeup of populations over time
• Developmental changes that occur in a single organism over the course of the life cycle are not a result of evolutionary change
• Relative fitness


  The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
• Selection indirectly favors certain genotypes by acting directly on phenotypes
• Three modes of natural selection

  • Directional selection
  • Disruptive selection
  • Stabilizing selection
• Microevolution


  A change in allele frequencies in a population over generations
• Three main mechanisms that cause allele frequency change


  • Natural selection
  • Genetic drift
  • Gene flow
• Only natural selection consistently causes adaptive evolution
• Individuals within all species vary in their phenotypic traits
• Variation in heritable traits is a prerequisite for evolution by natural selection
• Mendel's work on pea plants provided evidence of discrete heritable units (genes)
• Mutations generates genetic variation. Mutations occurs randomly with respect to organism's needs.
• Phenotypic variation often reflects genetic variation
• Genetic variation


  Differences in the composition of genes or other DNA sequences among individuals
• Sources of Genetic Variation


  • Formation of New Alleles
  • Altering Gene Number or Position
  • Rapid Reproduction
  • Sexual reproduction
• Genetic variation is required for a population to evolve but does not guarantee that it will evolve
• One or more factors that cause evolution must be at work for a population to evolve
• The Hardy-Weinberg equation can be used to test whether a population is evolving
• There are five conditions that must be must met for population not to evolve these are no mutations, random mating, no natural selection, extreme large population size and no gene flow
• Gene pool


  A population is a group of individuals that live in the same area and interbreed, producing fertile offspring
• Due to natural selection, some alleles may become more common than others in the gene pool
• Allele frequency


  A change in the relative frequency of different alleles in the gene pool
• Three major factors that alter allele frequencies and bring about most evolutionary change


  • Natural selection
  • Genetic drift
  • Gene flow
• Genetic drift


  A process where allele frequencies fluctuate unpredictably from one generation to the next
• Genetic drift reduces genetic variation through loss of alleles, especially in small populations
• Founder effect


  The founder effect occurs when a few individuals become isolated from a larger population
• Bottleneck effect


  The bottleneck effect can result from a drastic reduction in population size due to a sudden environmental change
• Effects of Genetic Drift


  • Genetic drift is significant in small populations
  • Genetic drift can cause allele frequencies to change at random
  • Genetic drift can lead to a loss of genetic variation within populations
  • Genetic drift can cause harmful alleles to become fixed