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How Evolution Works

How Evolution Works. Genes , Geography and Sex. Early Idea: Lamarckian Evolution. Fossil record indicated increasing complexity Reasoned traits are passed via use and disuse e.g. the giraffe’s neck. Step 1: Raw Material. Genes are raw material Forms of genes = alleles

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How Evolution Works

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  1. How Evolution Works Genes, Geography and Sex

  2. Early Idea: Lamarckian Evolution • Fossil record indicated increasing complexity • Reasoned traits are passed via use and disuse • e.g. the giraffe’s neck

  3. Step 1: Raw Material • Genes are raw material • Forms of genes = alleles • Polygenic vs. Single gene trait

  4. Selection on a Single Gene: The Peppered Moth • Before Industrial Revolution • After Industrial Revolution • Single gene controlling a trait will have only a few (usually 2 or 3 phenotypes)

  5. Variation and Selection • Variation from two sources 1) New mutations = new allele types 2) Gene shuffling = new allele combinations • Any change in allele frequency = Evolution • Peppered Moth Simulation

  6. Polygenic Traits • More than one gene controls a trait

  7. Selection and Changing the Norm • Most traits are polygenic • The normal trait is the average or mean in the population • Selection changes the mean, usually lowers variation • Selection will adjust mean

  8. Stabilizing Selection

  9. Disruptive Selection • Can lead to new species

  10. Does Evolution Ever Stop? • YES, but only if the following conditions are met 1) Random mating 2) Large Population 3) No movement in or out of population 4) No Mutations 5) No Natural Selection • Hardy Weinberg Equilibrium

  11. How New Species Are Formed • Two populations must become reproductively isolated

  12. Behavioral Isolation • Groups differ in mating, feeding, sleep/awake cycles so members of populations do not meet to mate

  13. Rana aurora (Red-legged frog) Ranacatesbiana(Common bullfrog) Breeds in still ponds • Breeds in fast moving streams

  14. Geographic Isolation

  15. Geological Time and Evolution • First fossils 3.5 bya Stromalites • 550 mya = Cambrian Explosion (by fossil evidence)

  16. Dating Fossil Age • Relative Dating • Radioisotope Dating • Known decay times of isotopes can be used

  17. Extinction and Adaptive Radiation • Most species cannot adapt • Those that can radiate into open niches

  18. Evolution Patterns Convergent Evolution Coevolution

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