Evolution

• Evolution

  A change in the average phenotype of a population
• Speciation

  The formation of a new species
• The founder effect

  When a small population becomes separated from the original population, so an allele in the small population becomes more frequent in succeeding generations
• Genetic drift

  A change in allele frequency because of chance. It is more likely to occur in small populations.
• Natural selection

  • Proposed by Charles Darwin and Alfred Wallace
  • Describes how phenotypes in a population can be maintained or changed to be optimal in the environment.
• Speciation by natural selection

  • Mutations in alleles lead to changes in allele frequencies.
  • Variation in phenotypes due to different alleles.
  • Many offspring are produced and there is competition for limited resources.
  • Selection pressures from the environment give some phenotypes a survival advantage and they survive long enough to breed, increasing their allele frequency.
• Deme

  A sub group of a population that interbreed more frequently, reducing gene flow with the rest of the population.
• allopatric speciation

  Evolution of a new species from demes isolated in different geographical locations
• Allopatric speciation

  caused by any mechanism of geographically separating demes
• Sympatric speciation

  Evolution of a new species from demes sharing the same geographical location. It leads to:

  • Behavioural isolation
  • Morphological isolation
  • Seasonal isolation
  • Hybrid sterility
• Behavioural isolation

  Demes with different courtship rituals will not interbreed and become isolated
• Morphological isolation

  If the genitalia of demes are incompatible they cannot interbreed
• Seasonal isolation

  Demes with different breeding seasons cannot interbreed and become isolated
• Hybrid sterility

  When 2 different species are similar enough to breed, they can produce hybrid offspring, but there are often sterile and unable to breed themselves.
• Prę zygotic isolation

  includes Seasonal isolation, behavioural isolation, morphological isolation and geographical isolation
• Post zygotic isolation

  involves hybrid sterility