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MECHANISMS OF EVOLUTION

MECHANISMS OF EVOLUTION. POPULATIONS, NOT INDIVIDUALS, EVOLVE. An organism cannot change its phenotype. A phenotype can become more predominant in a population, though. Gene Pool. All the alleles of the population’s genes. ALLELIC FREQUENCY.

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MECHANISMS OF EVOLUTION

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  1. MECHANISMS OF EVOLUTION

  2. POPULATIONS, NOT INDIVIDUALS, EVOLVE An organism cannot change its phenotype. A phenotype can become more predominant in a population, though.

  3. Gene Pool All the alleles of the population’s genes.

  4. ALLELIC FREQUENCY The percentage of any specific allele in the gene pool.

  5. GENETIC EQUILIBRIUM A population in which the allele frequencies remain the same over many generations.

  6. CHANGES IN GENETIC EQUILIBRIUM A population in genetic equilibrium is not evolving. When equilibrium of the gene pool is disrupted, evolution occurs.

  7. Changes in equilibrium may be the result of mutations.

  8. Gene Flow Organisms moving in (immigration) or out (emigration) of a population creates changes in the allelic frequencies of the gene pool.

  9. Hardy-Weinberg Principle • In order for genetic equilibrium to remain, these conditions must be met: • No mutations • No immigration or emigration • Random mating

  10. GENETIC DRIFT The alteration of allelic frequencies by chance events. Can greatly affect small populations.

  11. NATURAL SELECTION ACTS ON VARIATIONS

  12. THE EVOLUTION OF SPECIES

  13. SPECIATION • Occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment.

  14. PHYSICAL BARRIERS CAN PREVENT INTERBREEDING Geographic isolation Reproductive isolation

  15. CHANGE IN CHROMOSOME NUMBER

  16. SPECIATION CAN OCCUR QUICKLY OR SLOWLY

  17. GRADUALISM • The idea that species originate through a gradual change of adaptations. Example: horses in fossil record.

  18. PUNCTUATED EQUILIBRIUM • The idea that speciation occurs in rapid bursts with long periods of genetic equilibrium between. • Caused by abrupt temperature changes or introduction of a competitive species.

  19. PATTERNS OF EVOLUTION

  20. ADAPTIVE RADIATION • Many species evolve from a single species. • Example – Darwin’s finches and Hawaiian Island honeycreepers.

  21. DIVERGENT EVOLUTION • Two or more species with the same common ancestor become different species due to isolation.

  22. CONVERGENT EVOLUTION • Two species with different ancestors evolve similar traits due to selective pressures in the environment.

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