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  1. horse donkey Speciation mule

  2. Speciation A B baby • Defined: evolution of new species from an existing species • Species: group of organisms that can interbreed and produce fertile offspring • 5 factors that lead to evolution • Natural Selection • Gene flow • Mutations • Sexual selection • Genetic drift A B baby A B Sterile baby

  3. Gene Flow(Migration) • Defined: Movement of alleles from 1 population to another • Increases variations in a population • Keeps differing populations similar • If gene flow is prevented • No variations (alleles) exchanged • Populations are isolated • Organisms adapt to their own environment • Can lead to speciation

  4. Random DNA mutations Random DNA mutations Reproductive Isolation Different predators Different predators Different resources Different resources • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species • Geographic Isolation: • Organisms isolated by geographic barrier

  5. Kaibab Squirrel (Grand Canyon)

  6. California Salamanders: Evolution in Action

  7. Ancestral salamanders B A One species One species

  8. Fruit flies of the same species were placed into two separate cages Famous fruit fly experiment Once isolated, the 2 groups were fed different types of food Although isolated, the flies continued to live and reproduce for many generations When brought back together most separated during reproduction.

  9. Reproductive Isolation • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species • Geographic Isolation: • Organisms isolated by geographic barrier • Behavioral Isolation • Organisms isolated by differing mating rituals If the mating calls do not attract each other, will they reproduce? Is gene flow stopped?

  10. Birds of Paradise

  11. Human mating rituals

  12. Human mating rituals

  13. Human mating rituals

  14. Human mating rituals

  15. Human mating rituals

  16. Human mating rituals

  17. Reproductive Isolation • When populations are isolated for a long time…gene flow stops • When populations can no longer mate or no longer reproduce fertile offspring • Final step in the development of a new species • Geographic Isolation: • Organisms isolated by geographic barrier • Behavioral Isolation • Organisms isolated by differing mating rituals • Temporal Isolation • Organisms isolated by differing times of reproduction If one group mates during the spring… Is gene flow stopped? And the other mates during the fall…

  18. Genetic Drift • Defined: Changes in allele frequencies due to chance • NOT natural selection • The Bottleneck Effect • Results in a loss of genetic variation (alleles) • More likely in smaller populations • Example: Natural disaster • Pre-forest fire: Green is best adapted (blend better) • Post-forest fire: Brown more likely to reproduce • Survival UNRELATED to adaptations

  19. Review • What is speciation? • What leads to speciation? • What is gene flow? • What happens if gene flow is prevented? • How are temporal, behavioral, and geographic isolation different? • How are temporal, behavioral, and geographic isolation similar? • What are the 5 factors that lead to evolution?