3.2 natural selection

• why does natural selection occur?

  • competition between species
  • disease
• process of natural selection

  • genetic variation in population
  • due to mutation
  • different selection pressures
  • species gains advantageous allele
  • more likely to survive and reproduce
  • allele passed off to offspring
  • increasing allele frequency
• what is allele frequency?

  • total number of one allele in a gene pool
• types of adaptations

  • behavioural - changes to actions
  • anatomical - changes to the body structure
  • physiological - changes to body processes
• what is a niche?


  • organisms specific role in their environment
• what are the 2 types of speciation?


  • allopatric - geographical seperation
  • sympatric - seperation due to season,time,behaviour
• process of speciation


  • population split and reproductive isolation occurs
  • restricted gene flow
  • mutation causes genetic variation
  • change in environment and different selection pressure
  • species becomes adapted
  • survive and reproduce
  • change in allele frequency
  • 2 species bred - infertile offspring form
• what is antibiotic resistance?

  • when bacteria mutate and become resistant to antibiotics
  • due to random mutation
  • bacteria gain advantageous allele
  • survive and reproduce via binary fission
• how to tell if organism is part of same species?

  • can interbreed
  • produce fertile offspring
• how to tell if an organism is part of a different species?

  • interbreed
  • produce sterile offspring
  • have different mating behaviours