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Genetic variation and Evolution Chapter 20 Why are organisms well adapted to their habitats?

Genetic variation and Evolution Chapter 20 Why are organisms well adapted to their habitats? Creationist explanation (see section 21.7) Is a religious view Divine role “intelligent design” not scientifically testable Scientific explanation “evolution from common ancestor”

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Genetic variation and Evolution Chapter 20 Why are organisms well adapted to their habitats?

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  1. Genetic variation and Evolution • Chapter 20 • Why are organisms well adapted to their habitats? • Creationist explanation (see section 21.7) • Is a religious view • Divine role • “intelligent design” • not scientifically testable • Scientific explanation • “evolution from common ancestor” • ‘Natural Selection” • -- is testable 20.2 -- should know H-W equation and why it’s important -- we may come back to this 20.4 – understand the meaning of fitness, but we’ll not cover the mathematical aspects 20.5 – skip 20.6 – read on your own 20.8 – read on your own Read or listen to the The Firing Line 1997 Creation-Evolution Debate http://www.bringyou.to/apologetics/p45.htm Question Genetic Variation & Evolution

  2. Darwin was not first to describe evolution George Cuvier (1790) – Fossils & ‘Catastrophism’ Jean Lamarck (1809) -- Environmental influence Lamarck’s theory of “Inheritance of Acquired Traits” Question Genetic Variation & Evolution

  3. Modern explanations of why traits change over time (20.3) -- Frequency of genes in the population change 5 Agents (mechanisms) of change: 1. Genetic Mutation– random changes to DNA code -- creates variation in traits -- ‘raw material’ of all evolutionary mechanisms 2. Natural selection– mechanism proposed by Darwin -- environment selects certain traits Genetic Variation & Evolution

  4. Gene Flow Founder effect Bottleneck effect Agents of change, con’t Other agents of change 3. Gene flow -- movement of individuals between populations 4. Nonrandom mating -- organisms prefer to mate with certain individuals 5. Genetic drift -- chance may favor certain traits in a small population Founder effect – population isolation bottleneck effect – population catastrophe -- gene pool reduction Genetic Variation & Evolution

  5. What are the fundamental premises of • Darwin’s theory of “Natural Selection”? • Read Section about Evolution in Chapter 1 • “On the Origin of Species by Means of Natural Selection” • “Evolution” (a process) • does not equal “Natural Selection” (a process) • Natural selection occurs when: • 1) There exists genetically based variation (inheritable) • in the traits of a species. • 2) Organisms produce more offspring than can survive. • 3) The environment selects for those organisms • with the best adapted traits. • 4) Organisms best adapted to the environment will reproduce most successfully. Genetic Variation & Evolution

  6. How does Darwin’s ‘Natural Selection’ explain giraffe evolution? “Selective Pressures” “Adaptation” -- a noun and verb -- not an ecological term Genetic Variation & Evolution

  7. What is nature of genetic variation? (20.1) Genetic mutation DNA Polymorphisms Different ‘alleles’ Hardy-Weinberg equation (20.2) p2 + 2pq + q2 -- frequency of Alleles  frequency of traits -- can provide evidence for selection Genetic variation in Asiatic lady beetle Question Genetic Variation & Evolution

  8. What are examples of environmental selective pressures? • Predator-prey interactions • Competition for resources • Human impacts • Natural selection acts upon existing genetic variation • -- theory is not ‘teleological” • Wrong: • “In order to hide from predators, the dead-leaf • butterfly evolved a leaf-like appearance.” • Better: • “Predation selected for butterflies that most • resembled a dead leaf.” • The environment selects among but • does not create variations! Question Genetic Variation & Evolution

  9. Do organisms always produce more offspring than can survive? Cichlides: Carmagnola Grey rabbit: Humans: 250,000 eggs 5-8 litters x 7 offspring 2- 7 children/family Genetic Variation & Evolution

  10. Why don’t humans evolve wings? Limits of Selection Existence genetic variation Complex traits involve many genes Suitable selective pressures Genes have multiple effects -- developmental genes Question Genetic Variation & Evolution

  11. All these crops are varieties of the species Brassica napa What is ‘Artificial Selection’? Are humans still evolving? Colors represent different genetic types. Map shows genetic variation in Africa. Group project Genetic Variation & Evolution

  12. Why does ‘in breeding’ cause genetic problems? • speciesnon-inbred inbred • Zebra lived 20 3 • died 7 2 • Eld’s deer lived 13 0 • died 4 7 • Giraffe lived 11 2 • died 3 3 • Oryx lived 35 0 • died 2 5 • Dorcas lived 36 17 • gazelle died 14 25 • From Klug & Cumminings Genetics 5th ed Genetic Variation & Evolution

  13. What are the effects of Natural Selection on a population? (20.7) “Microevolution” vs “Macorevolution” Genetic Variation & Evolution

  14. What is the effect of Directional Selection on a population? Progressive change in a trait within a species Genetic Variation & Evolution

  15. How does Stabilizing Selection affect a population? Human birth weight & Eurosta gall size Stabilizing selection & ‘living fossils’ Genetic Variation & Evolution

  16. How does Disruptive Selection affect a population? Responsible for divergence of a single species into two different species Modern example of process: blackbellied seedcracker Question Genetic Variation & Evolution

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