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Understanding Evolution: Genes, Selection, and the Formation of New Species**

This comprehensive overview of evolutionary biology delves into the mechanisms of evolution, emphasizing the role of genes, natural selection, and environmental factors. From early ideas like Lamarckian evolution to modern understandings of genetic variation and speciation, the text explores core concepts such as the peppered moth example, polygenic traits, and stabilizing versus disruptive selection. It discusses the conditions for evolution to halt and the processes that lead to reproductive isolation and new species formation, alongside insights on fossil dating and patterns in evolution.

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Understanding Evolution: Genes, Selection, and the Formation of New Species**

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Presentation Transcript

  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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