HARDY-WEINBERG QUIZ

• Hardy-Weinberg Assumptions & Equations


  • Mating must be completely random
  • No mutation
  • No immigration or emigration
  • Population must be large (infinitely large)
  • No natural selection

  
• Possible mechanisms of population change


  • Mutations
  • Sexual reproduction - random assortment, crossing over, random fertilization
• Evolution is not change in individuals
• Hardy-Weinberg Equilibrium

  Both allele frequency and genotype frequency will remain unchanged (in equilibrium) unless outside forces change those frequencies
• Breaking Assumption 1: Mating must be completely random


  Sexual dimorphism
• Breaking Assumption 2: No mutation


  Any change to the sequence of nitrogen bases - including errors in replication or transcription
• Breaking Assumption 3: No immigration or emigration
• Breaking Assumption 4: Population must be "large" (infinitely large)


  Any population that is not infinitely large - will affect size - smaller population is the more random chance will play a part in population changes
• Breaking Assumption 5: No natural selection (no fitness advantage)


  Survival and reproduction
• The only force responsible for adaptive change is natural selection
• Three major factors alter allele frequencies and bring about most evolutionary change:

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

  Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions
• Natural selection is the mechanism of evolution, and it is not random. Nature - the environment - selects/determines which organisms survive and reproduce. It is the only process that causes adaptive change, making populations better suited to their environment.
• Genetic Drift

  Allele frequencies fluctuate unpredictably from one generation to the next. The smaller the population, the more prone to drift and the greater the chance of deviation from a predicted result by chance alone. Genetic drift tends to reduce genetic variation through losses of alleles.
• Founder Effect

  Occurs when a few individuals become isolated from a larger population. Allele frequencies in the small founder population can be vastly different from those in the larger parent population.
• Bottleneck Effect

  A sudden reduction in population size due to a change in the environment. The resulting gene pool may no longer be reflective of the original population's gene pool. If the population remains small, it may be further affected by genetic drift.
• The Hardy-Weinberg Equilibrium may not allow us to accurately predict future changes since many of the assumptions will not be true
• Genetic Drift is a random process
• Gene Flow

  (immigration/emigration) is a random process that could change allele frequencies in a population
• Three modes of selection

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

  • Favors individuals at one end of the phenotypic range
• Disruptive selection

  • Favors individuals at both extremes of the phenotypic range
• Stabilizing selection


  • Favors intermediate variants and acts against extreme phenotypes
• Adaptive evolution occurs as the match between an organism and its environment increases
• Because the environment can change, adaptive evolution is a continuous process
• Speciation, the origin of new species, is at the focal point of evolutionary theory
• Evolutionary theory must explain how new species originate and how populations evolve
• Microevolution


  Changes in allele frequency in a population over time
• Macroevolution


  Broad patterns of evolutionary change above the species level
• Biological species concept


  A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations
• Gene flow between populations holds the phenotype of a population together
• Reproductive isolation


  The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
• Hybrids


  The offspring of crosses between different species
• Prezygotic barriers


  • Habitat Isolation
  • Temporal Isolation
  • Behavioral Isolation
  • Mechanical Isolation
  • Gametic Isolation
• Habitat isolation


  • Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
• Temporal isolation


  • Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
• Behavioral isolation


  • Courtship rituals and other behaviors unique to a species are effective barriers
• Mechanical isolation


  • Internal differences can prevent successful mating
• Gametic Isolation


  • Sperm of one species may not be able to fertilize eggs of another species
• Postzygotic barriers


  • Reduced Hybrid Viability
  • Reduced Hybrid Fertility
  • Hybrid Breakdown