Speciation/Evolution Slides

• Species

  A group of organisms whose members possess similar anatomical characteristics and have the ability to interbreed to produce viable, fertile offspring
• Natural Selection

  • Individuals possess variations
  • Variations are heritable
  • More individuals exist than can survive
  • Survival and reproduction are dependent on adaptation to environment (fitness)
  • The history of the earth is long
  • There is geologic time
• Conditions for Evolution

  • Mutation
  • Gene flow
  • Natural Selection
  • Non-random mating
• Mutation


  Random changes to the DNA code
• Gene flow

  Flow of genetic material between populations
• Natural Selection

  Only the best adapted individuals survive & reproduce
• Non-random mating

  Mating decisions can be based on fitness or aesthetics
• Speciation


  The evolution of new species, occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment
• Barriers to species interactions

  • Pre-zygotic: temporal, behavioral, mechanical, gametic
  • Post-zygotic: hybrid inviability and sterility
• Allopatric speciation

  Populations become separated by a geographic barrier
• Sympatric speciation

  Groups are isolated reproductively without being separated geographically
• Polyploidy


  A change in chromosome number can prevent organisms from reproducing successfully
• Gradualism

  Gradual change in adaptations over time
• Punctuated Equilibrium

  Rapid bursts of speciation followed by long periods of genetic equilibrium
• Causes of Punctuated Equilibrium

  • Introducing new competitive species
  • Climate change
• Types of Natural Selection

  • Stabilizing selection
  • Directional selection
  • Disruptive selection
• Stabilizing selection

  Favors an average (reduces variation)
• Directional selection

  Favors one extreme (rapid evolution)
• Disruptive selection

  Favors both extremes (leads to 2 new species)
• Divergent evolution


  The pattern of evolution in which species that once were similar to an ancestral species, become increasingly different
• Adaptive radiation

  Species adapted to an array of habitats
• Convergent evolution

  The process whereby organisms (plants too) not closely related, independently evolve similar traits as a result of having to adapt to similar environments
• Analogous structures

  Similar structures that evolved independently in different species
• Populations evolve, not individuals
• Gene pool


  All the possible alleles in a population
• Allelic frequency

  The percentage of any allele in a gene pool
• p represents the frequency of a dominant allele, while q represents the frequency of a recessive allele
• p + q = 1
• Genetic equilibrium

  The frequency of alleles remains the same over generations
• Causes of disruption to genetic equilibrium

  • Useful variations caused by mutations
  • Natural selection
  • Genetic Flow: populations gain or lose alleles
  • Genetic Drift: the alteration of allele frequencies by random chance
• Genetic Flow

  Populations gain or lose alleles
• Genetic Drift

  The alteration of allele frequencies by random chance
• Founder effect


  New populations established by a few founding individuals also have gene frequencies that differ from those in the parent population
• Bottleneck effect


  Organisms of normally large populations may pass through periods (bottlenecks) when only a small number of individuals survive