Please enable JavaScript.

Coggle requires JavaScript to display documents.

17.2 Natural selection - Coggle Diagram

- - - - Alleles for antibiotic resistance often occur on plasmids
      - The more antibiotics are used, the greater the selection pressure we exert on bacteria to evolve resistance
      - Antibiotics causing directional selection, with bacteria with alleles for antibiotic resistance surviving and multiplying
    - - Originally, peppered moths were white with dark speckles
      - A random mutation resulting in a new dominant allele gave rise to the black moth
      - Main selection pressure for moths is birds
      - In industrial areas, lichen could not grow on trees so dark tree bark was exposed beneath
        
        Moths with white allele were more easily spotted by birds
        
        White moths were less likely to survive and reproduce
        
        White allele frequency decreased
        
        Black moths were spotted less and therefore had a higher survival rate
        
        Black allele frequency increased
        
        Directional selection
      - In other areas, lichen could still grow as normal
        
        Moths with white allele were more camouflaged than moths with black allele
        
        No changes in allele frequency
        
        Stabilising selection