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Unit 5 Evolution

Unit 5 Evolution. Ch. 16 Evolution of Populations. Sources of Genetic Variation. The 2 main sources of genetic variation are mutations & the genetic shuffling that results from sexual reproduction. Single-Gene & Polygenic Traits.

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Unit 5 Evolution

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  1. Unit 5 Evolution Ch. 16 Evolution of Populations

  2. Sources of Genetic Variation • The 2 main sources of genetic variation are mutations & the genetic shuffling that results from sexual reproduction

  3. Single-Gene & Polygenic Traits • The # of phenotypes produced for a given trait depend on how many genes control the trait • Single-gene trait - controlled by a single gene, that has 2 alleles • Ex.) Widow’s Peak

  4. Single-Gene & Polygenic Traits • Polygenic traits - trait controlled by 2 or more genes • Ex.) Height in humans

  5. Evolution as Genetic Change • Evolutionary fitness can be viewed as an organism’s success in passing genes to the next generation • Evolutionary adaptation can be viewed as any genetically controlled trait that increases an individual’s ability to pass along its genes

  6. Evolution as Genetic Change • NS never acts directly on genes • NS can only affect which individuals survive & reproduce, & which do not • Also, remember that it is populations, not individual organisms, that can evolve over time

  7. NS on Single-Gene Traits • NS on single-gene traits can lead to changes in allele frequencies & thus to evolution

  8. NS on Polygenic Traits • NS can affect the distributions of phenotypes in any of 3 ways: directional selection, stabilizing selection, or disruptive selection

  9. NS on Polygenic Traits • Directional Selection - occurs when individuals at 1 end of the curve have higher fitness than individuals in the middle or at the other end

  10. NS on Polygenic Traits • Stabilizing selection - occurs when individuals near the center of a curve have higher fitness than individuals at either end

  11. NS on Polygenic Traits • Disruptive selection - when individuals at the upper & lower ends of the curve have higher fitness than individuals near the middle

  12. Evolution vs. Genetic Equilibrium • Genetic equilibrium - when allele frequencies remain constant, the population will not evolve • 5 conditions are required to maintain genetic equilibrium: random mating, large population, no movement into/ out of population, no mutations, & no NS

  13. The Process of Speciation • Speciation - formation of a new species • The gene pools of 2 populations must become separated for them to become new species

  14. Isolating Mechanisms • As new species evolve, populations become reproductively isolated from each other • Reproductive isolation - when members of 2 populations can’t interbreed & produce fertile offspring

  15. Isolating Mechanisms • Behavioral isolation - when 2 populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior • Ex.) Birds with different mating songs

  16. Isolating Mechanisms • Geographic isolation - 2 populations are separated by geographic barriers like rivers, mountains, or bodies of water • Ex.) Squirrels split by Colorado River

  17. Isolating Mechanisms • Temporal isolation - when 2 or more species reproduce at different times • Ex.) Orchids releasing pollen on different days

  18. Testing NS in Nature

  19. Speciation in Darwin’s Finches • Speciation in the Galapagos finches occurred by: • founding a new population • geographic isolation • changes in the new population’s gene pool • reproductive isolation • ecological competition

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