Genetic diversity and adaptation

• Natural selection


  - the process that leads to evolution in populations

  - results in species becoming better adapted to their environment
• Gene pool


  - all the genes and alleles in a population at a particular time
• Allele frequency


  - the proportion of organisms within the population carrying a particular allele
• Evolution


  - the change in allele frequency

  - over many generations in a population
• Selection pressure


  - factors that affect the survival of an organism

  - the driving force of natural selection
• Types of selection


  - stabilising

  - directional
• Directional selection


  - one of the extreme traits has a selective advantage

  - occurs when there is a change in the environment

  - the modal trait changes
• Stabilising selection


  - the middle (median) trait has a selective advantage and continues to be the most frequent in the population

  - represented by a normal distribution graph

  - range decreases as the extreme traits are lost over time
• An example of directional selection


  antibiotic resistance in bacteria

  
• An example of stabilising selection


  human birth weights