The founder effect describes when a small group of individuals separates from a larger group and expresses genes that were rare in the original population. If this happens, the rare gene or genes start to become common in the next generations. In contrast, the bottleneck effect happens when a random catastrophe like an earthquake kills off most of a population. In this situation, the genes in the surviving population occur randomly. The common thread that runs through both the founder effect and the bottleneck effect is that they reduce the amount of genetic diversity in a population.

Comparison Chart

Founder EffectBottleneck Effect
Reduces genetic diversityYesYes
CauseSeparation of a small group of individuals from a larger population.The destruction of most of a population.
Results in a random sample of genes from the original population.NoYes
Probability of inbreedingHighVery high
Can result in speciationYesYes
  • Fumarase deficiency in Mormons.
  • Tay-Sachs disease in some Jewish populations.
  • High incidence of deaf individuals in Martha‚Äôs Vineyard.
  • The origination of man in Africa and his migration to other parts of the world.
  • Artificially induced by the selective breeding of cats, dogs, cattle, horses, etc.
  • Any endangered species are going through a bottleneck event.
  • The recovery of the European Bison from the brink of extinction and their current reproductive difficulties.


  • Brennan, J. (Updated April 25, 2017). Comparison of the bottleneck effect and the founder effect. Retrieved from
  • The Microevolution Debate: Bottleneck Effect vs Founder Effect. (n.d.). Retrieved December 27, 2017 from