Types of selection

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Selection:

  • Process by which organisms that are better adapted to an environment tend to survive and breed
  • Most characteristics are controlled by several genes (polygenes)
  • Depending on which characteristics are favoured selection will produce different results

Normal distribution:

  • Bell shaped curve
  • Data tends to be around a central value with no bias left or right
  • Mean, median and mode are the same value
  • Standard deviation is a measure of how spread out data is

Directional selection:

  • A phenotype on one side of the mean becomes better adapted due to a change in the environment
  • As they are better adapted they are more likely to survive and breed
  • With more offspring there is an increase in allele frequency
  • Over time the mean will move in that direction
  • One extreme is selected for while the other extreme is selected against

Directional selection - Antibiotic resistance:

  • Antibiotics quickly became less effective at killing bacteria
  • Populations of bacteria were

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