Evolution

• Evolution is the change in allele frequency in a population.
• Predation, competition and disease are selection pressures.
• Disruptive selection - both extreme values are selected for and the mean value is selected against.
• Gene pool - all of the alleles of the genes in a population
• Population - as a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.
• Allopatric speciation is when new species develop due to geographical isolation.
• Sympatric speciation is the development of new species due to reproductive isolation but not due to geographical isolation.
• Allopatric Speciation

  • geographical speciation of two populations - no interbreeding
  • variation already present due to mutations
  • selection of different features and hence advantageous alleles
  • selection pressures (identify)
  • survival and reproduction
  • different frequency of alleles
  • separate gene pools / no interbreeding
• Isolating mechanisms:

  temporal - different breeding seasons.

  ecological/behaviour - different courtship behaviours, different niches/ habitats/ feeding areas.

  mechanical - mismatch of reproductive organs.

  gamete incompatibility - sperm killed in female's reproductive tract.
• Sympatric Speciation

  • name isolating mechanism
  • variation already present due to mutations.
  • different selective pressures operate/ changes in allele frequency divergence of gene pools
  • selection of different features and hence different alleles
  • survival and reproduction
  • different frequency of alleles
  • separate gene pools / no interbreeding