Natural Selection

• What is natural selection?

  The process where advantageous alleles survive
• How do advantageous alleles affect a population over generations?

  They become more common in the population
• What is directional selection?

  • Favors one extreme of a trait
  • Shifts the population’s mean in that direction
  • Example: Antibiotic resistance in bacteria
• What is stabilising selection?

  • Favors the average phenotype
  • Selects against extremes
  • Example: Human birth weight
• What are the three types of adaptations?

  1. Anatomical – physical structures (e.g. white fur on a polar bear)
  2. Physiological – internal processes (e.g. chameleons changing colour)
  3. Behavioural – actions (e.g. birds migrating south in winter)
• How do mutations contribute to evolution?

  They create new alleles that may be beneficial
• What happens if a mutation is beneficial?

  Natural selection may increase its frequency
• How does natural selection lead to evolutionary change?

  • Beneficial alleles increase in frequency
  • Over generations, these alleles become common
  • Results in adaptation to the environment
• Why are aseptic techniques important in microbial growth investigations?

  They prevent contamination from other microorganisms
• What is the first step in testing antibiotic effectiveness using paper discs on an agar plate?

  • Inoculate the agar plate
  • Spread bacteria evenly with an inoculating loop
  • Create a "lawn" of bacteria
• What should you do after inoculating the agar plate in antibiotic testing?

  • Soak paper discs in different antibiotics
  • Place discs on the agar plate
  • Ensure discs do not touch each other
• What occurs during the incubation phase of the antibiotic test?

  • Plate incubated at 30°C for 24 hours
  • Bacteria grow and interact with antibiotics
• What does a clear zone around an antibiotic disc indicate?

  It indicates the antibiotic is effective
• What is the purpose of a negative control in antibiotic testing?

  • Ensures observed effects are due to the antibiotic
  • Confirms results are not influenced by other factors