Natural selection

• What are the facts of reproductive success?

  1. All organisms produce more offspring than can be supported
  2. The gene pool contains a wide variety of alleles
  3. All organisms face selection pressures
• What does overproduction lead to?

  Competition for food and breeding sites, increased predators and disease
• Intraspecific

  within a species
• Interspecific

  Across multiple species
• What is the process of natural selection?

  1. Selection pressure
  2. Successful alleles
  3. Passed on to next generation
  4. Frequency of alleles increases
  5. Successful phenotypes increases
• What is directional selection?

  A response to a changing environment, where a species becomes more extreme
• What is stabilising selection?

  Occurs in a stable environment where species become more average
• What are 2 examples of directional selection?

  • Bacterial resistance to antibiotics (MRSA)
  • Rats becoming resistant to rat poison (warfarin), but needing more vitamin K
• What are 2 examples of stabilising selection?

  • The deep ocean- greenland shark and the coelacanth
  • Human baby weight
• What is disruptive selection?

  An environmental change produces selection pressures that favour two, opposing extremes
• What is an example of disruptive selection?

  Peppered moths