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Evolution

Evolution. Chapters 19 through 22. Learning Objectives. Compare microevolution to macroevolution Define and discuss natural selection Relate Darwin’s contributions to our overall understanding of evolution Compare phenotype and genotype

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Evolution

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  1. Evolution Chapters 19 through 22

  2. Learning Objectives • Compare microevolution to macroevolution • Define and discuss natural selection • Relate Darwin’s contributions to our overall understanding of evolution • Compare phenotype and genotype • Apply the Hardy-Weinberg equation to populations undergoing a shift in equilibrium

  3. Learning Objectives • Define Convergence, Divergence, Polymorphism, and Sexual Dimorphism • Discuss speciation • Explain prezygotic and postzygotic mechanisms for speciation

  4. Nature Changes • Biogeography • World distribution of organisms • Global exploration raised difficult questions for “unchanging creation” • Comparative morphology revealed structural similarities in “dissimilar” anatomies • Vestigial structures currently useless structures

  5. Large, Flightless Birds

  6. Humerus Ulna Radius Carpals 5 1 1 4 Digits 5 2 2 5 3 4 2 3 4 3 Wing of bat Foreleg of pig Flipper of dolphin Fig. 19-3, p.403

  7. 19.2 Darwin’s Journeys • Darwin saw the world on the voyage of the Beagle • Darwin used common knowledge and several inferences to develop his theory • Darwin’s theory revolutionized the way we think about the living world

  8. Darwin and the Beagle • 1831 voyage of H.M.S. Beagle • Timed well with modern geology • Darwin observed global biogeography • Fossils similar to extant organisms • Organisms near each other similar even if in different habitats • Species change after isolation from ancestral groups

  9. Ancestors and Descendants

  10. Ancestors and Descendants

  11. Morphological Differences

  12. Developing Darwin’s Theory • Darwin tried to discover how species arise • Finch island biogeography • Artificial selection • Process of improving organisms by selective breeding • Darwin tried to reconcile observation of artificial selection with nature

  13. Struggle for Existence • Struggle for existence occurs when resources limit reproduction of organisms • All species reproduce faster than needed to replace parent generation

  14. Natural Selection • Natural selection increases favorable hereditary traits in successive generations • Adaptive traits are genetic characteristics that increase likelihood of reproduction • Evolutionary divergencecreates new species over long time periods

  15. Darwin’s Observations and Inferences

  16. Darwin’s Revolutionary Theory • Darwin provided physical rather than spiritual explanations • Evolutionary change occurs in populations • Evolution is a multistage process • Variations, natural selection, inheritance • Organisms function best in particular environments

  17. Early Theory of Evolution Tests • Two perceived problems tested theory of evolution: • Darwin used complex trait examples, Mendel simple traits • Darwin studied gradual evolution, Mendel’s mutations of simple traits had fast impact • Population genetics linked Darwinian evolution and Mendelian genetics

  18. Modern Synthesis • Modern synthesis unified theory of evolution • Combined all areas of biology under evolution • Gradualism more important than dramatic change • Microevolution of populations and macroevolution of life history act in concert

  19. Evidence of Evolutionary Change • Adaptation by natural selection • Long term evolutionary trends across species (wings) • Short term evolutionary trends within populations (antibiotic and pesticide resistance) • Fossil Record • Biological lineages such as birds from dinosaurs

  20. 1. When mosquitoes were first exposed to DDT, only about 5% of the population was resistant and the insecticide killed the remaining 95%. 2. Resistant individuals survived and reproduced, passing the genes for resistance to the next generation. 3. One year later, about 50% of the population was resistant. The same concentration of DDT killed only 50% of the population. 4. Resistant individuals again survived and reproduced. Percentage killed 5. After just a few more months, about 75% of the population was resistant and the same concentration of DDT killed only 25% of the population. Months Fig. 19-11, p.412

  21. Bird Ancestry

  22. Evidence of Evolutionary Change • Historical biogeography • Study of organismal distribution in relation to evolutionary history • Island and continental biogeography • Comparative morphology analyzes extant and extinct structural relationships • Homologous traits similar between species due to common ancestry • Human and bat forelimbs

  23. Evidence of Evolutionary Change • Comparative embryology has shown embryos from major groups developmentally similar • Gill pouches in humans and fish • Genetic code independent evidence of evolutionary relationships • Closely related species have closely related amino acid, nucleotide sequences

  24. Human embryo Adult shark Fig. 19-13, p.414

  25. Differences in Amino Acid Sequences INSERT FIG 19.14 HERE

  26. Macroevolution • Microevolution is small changes within a species; creating new alleles • Macroevolution are large changes over a geological time period that lead to speciation

  27. Phenotype vs. genotype • Genotype= the genetic makeup of alleles of an individual • Homozygous=pp, qq • Heterozygous=pq • Phenotype= the expressed alleles • pp=white, qq=black, pq=grey • Some alleles are dominant, some recessive, and some partial

  28. Hardy-Weinberg Equilibrium • p2 +2pq + q2 = 1.0 • If a population has 70% p alleles, then q must be at 30% • Evolution is a process resulting in changes of genetic makeup over time • Evolutionary agents are those that disrupt the Hardy-Weinberg equation

  29. Speciation • Speciation • Process of species formation • Inferred by studying products, species • Microevolutionary processes that lead to population divergence produce new species

  30. Morphological Species Concept • Based on differences in anatomical features • Only species definition for fossils • May lead to erroneous conclusions • Some anatomical differences within species • Some species identical in appearance • Not always evolutionarily based

  31. Biological Species Concept • Based on reproductive isolation • If populations can interbred, they are members of same species • If populations do not make fertile offspring, they are different species • Problems with biological species • Asexual and extinct organisms

  32. Subspecies

  33. Prezygotic Mechanisms • Ecological isolation from habitats • Temporal isolation from mating timing • Behavioral isolation from mating signals, sexual selection • Mechanical isolation from reproductive structures • Gametic isolation from gamete incompatibility

  34. Interspecific Hybrids

  35. Postzygotic Isolating Mechanisms • Interspecies offspring reproductively isolated if less fit than intraspecies offspring • Hybrid inviability from species hybrids not surviving • Hybrid sterility from species hybrids • Hybrid breakdown reduced fitness of F2

  36. Macroevolution • Microevolution is small changes within a species; creating new alleles • Macroevolution are large changes over a geological time period that lead to speciation

  37. Convergent/Divergent Evolution • Convergence=Similar adaptations in distantly-related organisms- Similar selective pressures produce similar adaptations • Divergence= Very distinct differences in closely related organisms • Polymorphism- differences within a species • Sexual Dimorphism- differences between male and females of a species

  38. Adaptive Radiation • Biodiversity • Number of species in given area • Adaptive radiation • Group of closely related species occupying different habitats • Ancestral species move into unfilled adaptive zone (unoccupied or open from extinction)

  39. Extinctions • Background extinction rate • Low rate, from environmental change and poor adaptations • Over global time scales, most species go extinct • Mass extinctions • High rate over short time • Climate changes from geological activity and asteroid impacts

  40. Evo-Devo • Evolutionary developmental biology (evo-devo) • Evolution in genes of embryonic development • Genes of development also regulate morphology • Homeoticgenes • Control transcription of development genes • Small changes in homeotic genes can produce large changes in morphology

  41. Homeotic Genes • Many organisms share common genetic tool-kit for development • Common animal genes for 500 million years • Common genes in animals, plants, fungi and prokaryotes from earliest life

  42. Hox Genes • Control animal body plan • Homeobox • 180-nucleotide sequence • Codes for homeodomain (part of a transcription factor)

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