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horse

horse. donkey. Speciation. mule. Speciation. Defined : evolution of a new species Species : group of organisms that can interbreed and produce fertile offspring Factors that lead to evolution Natural Selection Gene flow Mutations Sexual selection Genetic drift. Gene Flow.

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horse

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  1. horse donkey Speciation mule

  2. Speciation • Defined: evolution of a new species • Species: group of organisms that can interbreed and produce fertile offspring • Factors that lead to evolution • Natural Selection • Gene flow • Mutations • Sexual selection • Genetic drift

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

  4. Genetic Drift • Defined: Changes in gene pool due to chance (not natural selection) • More likely in smaller populations • Ex: Forest fire destroys 90% of a forest • Survival unrelated to adaptations • Pre-forest fire (left picture): Blue is more advantageous • Post-forest fire (right picture): Due to more red survivors, red has the advantage to reproduce in this new environment

  5. Geographic Isolation • Mountains, rivers, canyons, oceans may separate apopulation • Natural selection allows favorable organisms to survive in different environments • Each population adapts to its isolated environment • Because isolated, no gene flow

  6. Kaibab Squirrel (Grand Canyon)

  7. Founder Effect: 14 Species of Galapagos Finches A B B D D C C

  8. Behavioral Isolation • Although not geographically separated, reproduction is prevented • 1) Different mating rituals • 2) Use of pheromones • No gene flow: differing populations unable to reproduce

  9. Temporal Isolation • Although not geographically separated, reproduction is prevented • 1) Mate at different seasons • 2) Some nocturnal • No gene flow: differing populations unable to reproduce

  10. End Result: Reproductive Isolation • Created as a result of behavioral, geographical, & temporal isolation • No mating between populations (no gene flow) • Two groups unable to reproduce • Sex organs don’t match, rituals don’t attract, physically separated • Species: group of organisms that can interbreed and produce fertile offspring

  11. Quick Review • New species are created (speciation) when populations become isolated • A changing or new environment greatly affects natural selection

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