Chance Changes in Genes

• Genetic Drift


  Occurs in small populations. Has a bigger impact on smaller gene pools.
• Genetic Drift


  Some genes become more or less common as individuals that carry them produce more offspring as a result of change rather than an actual adaptive advantage.
• Alleles in Genetic Drift


  Alleles can become fixed or lost by genetic drift, decreasing genetic diversity.
• Founder Effect


  Occurs when small number of individuals establish a new population. The gene pool will reflect genotypes of found individuals.
• Founder Effect


  Is not representative of the original populations genetic diversity. The individuals are reproductively isolated from the original population.
• Genetic variation in Founder Effect

  Genetic variation is reduced, but otherwise rare genes may be common simply because they were carried by 'founders'.
• Bottleneck Effect


  When a population becomes very small and then expands. The new gene pool will reflect the genotypes of individuals at the bottleneck. (This is important consideration for endangered species).
• Small Populations


  Smaller populations have less genetic variation to counteract natural selection pressures.
• Small Populations


  Smaller populations means a higher chance of inbreeding which means less genetic diversity.