Selection

• What do stabilising and directional selection affect?


  Allele frequency

  - affect this in different ways
• What is stabilising selection?


  Where individuals with alleles for characteristics towards the MIDDLE OF THE RANGE are more likely to survive and reproduce
• When does stabilising selection occur??


  When the environment is NOT changing
• What does stabilising selection do?


  REDUCES THE RANGE OF POSSIBLE PHENOTYPES
• stabilising selection

  
• What is directional selection?


  Where individuals with alleles for a SINGLE EXTREME PHENOTYPE are more likely to survive and reproduce
• When may directional selection occur?


  In response to an environmental change
• directional selection

  
• What is disruptive selection?


  Where individuals with alleles for extreme phenotypes at EITHER END OF THE RANGE are more likely to survive and reproduce
• Disruptive selection is the opposite of what?


  stabilising selection
• Why is disruptive selection the opposite of stabilising selection?


  Because characteristics towards the MIDDLE of the range are LOST
• When does disruptive selection occur?


  When the environment favours more than one phenotype
• Disruptive selection