07 evolution without selection

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07 evolution without selection

  1. 1. Evolution Without Selection
  2. 2. Evolution Without Selection Genetic Drift: Occurs when a population is so small that allele frequencies may be altered by random chance with no selective pressures. Imagine a beetle population where 40% are green and 60% are brown
  3. 3. Evolution Without Selection A random catastrophe has reduced the beetle population's size. Now 25% are green and 75% are brown.
  4. 4. Evolution Without Selection If the last few green beetles fail to pass on their green allele, the allele may be lost forever.
  5. 5. Genetic Drift A certain allele may become extremely common or disappear entirely. (by chance – recall Punnett squares and probabilities of passing down traits)
  6. 6. Genetic Drift This results in reduced genetic diversity in the population. The low worldwide population of white-collared lemurs has reduced their genetic diversity.
  7. 7. Genetic Drift There are 2 major reasons for population reduction leading to genetic drift: 1) Genetic Bottleneck 2) Founder Effect
  8. 8. Think. Pair. Share. Under what circumstances would a small group of organisms become the foundation of a new population? Where did this small group of organisms come from? Consider the terms below. 1) Genetic Bottleneck 2) Founder Effect
  9. 9. Genetic Bottleneck 1) A genetic bottleneck occurs when a species' population is drastically reduced.
  10. 10. Genetic Bottleneck The survivors must reestablish the population using a very limited gene pool.
  11. 11. Genetic Bottleneck The members of this new population exhibit little genetic variation. This is usually what happens in many endangered species such as the Iberian lynx.
  12. 12. The Founder Effect 2) The founder effect occurs when small group from a population moves to a new location.
  13. 13. The Founder Effect That small group will reproduce to populate the new location. Genetic variation will be low.
  14. 14. The Founder Effect Original population 3 random animals with this combination of alleles wanders away Alleles of original population
  15. 15. The Founder Effect Animals that moved create a new population in a new location

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