Chap 27 evolution

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Evolution Pt 2 notes ( we only did last half)

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Chap 27 evolution

  1. 1. Chapter 27: Evolution of Life 27- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Evidence of Evolution <ul><li>Evolution is all the changes that have occurred in living things since life began. </li></ul><ul><li>The earth is 4.5 billion years old, and prokaryotes evolved 3.5 billion years ago. </li></ul><ul><li>The eukaryotic cell arose 2.1 billion years ago, but there was no multicellularity until 700 million years ago. </li></ul>27-
  3. 3. <ul><li>Evolution encompasses common descent and adaptation to the environment. </li></ul><ul><li>Due to common descent, all living things share common characteristics: they are made of cells, take chemicals and energy from the environment, respond to external stimuli, reproduce, and evolve. </li></ul><ul><li>Many fields of biology give evidence that evolution has occurred. </li></ul>27-
  4. 4. Fossil Evidence <ul><li>Fossils are the remains of past life, usually consisting of hard parts, such as shells, bones, or teeth. </li></ul><ul><li>Most fossils are found embedded in sedimentary rock . </li></ul><ul><li>Sedimentation causes rock formation as particles accumulate in layers; any given stratum (layer) is older than the one above it, and younger than those below. </li></ul>27-
  5. 5. <ul><li>Paleontologists are biologists who study fossils. </li></ul><ul><li>Certain fossils serve as transitional links between groups. </li></ul><ul><li>Such fossils allow paleontologists to deduce the sequence in which certain groups evolved (i.e., fishes evolved before amphibians, which came before reptiles, which evolved before both birds and mammals). </li></ul>27-
  6. 6. Transitional fossils 27-
  7. 7. <ul><li>Geological Time Scale </li></ul><ul><li>As a result of studying strata across the earth, scientists have divided earth’s history into eras , periods , and epochs . </li></ul><ul><li>There are two ways to date fossils: </li></ul><ul><li>Relative dating provides an approximate age based on position of the fossil within rock strata. </li></ul><ul><li>Absolute dating uses radioactive isotopes to measure the amount of radiation left in a fossil, yielding an actual age. </li></ul>27-
  8. 8. <ul><li>Carbon 14 ( 14 C) is the only radioactive isotope in organic matter. </li></ul><ul><li>The amount of radioactivity remaining in a fossil can be compared with that of a modern sample to determine the age of a fossil. </li></ul><ul><li>Radioactive isotopes decay at a known rate; the half-life of a radioactive isotope is the length of time it takes for half of the radioactive isotope to change into another stable element. </li></ul>27-
  9. 9. <ul><li>Mass Extinctions </li></ul><ul><li>Extinction refers to the death of every member of a species. </li></ul><ul><li>During a mass extinction , a large percentage of species become extinct within a relatively short period of time. </li></ul><ul><li>Mass extinctions occurred at the ends of the Ordovician, Devonian, Permean, Triassic, and Cretaceous periods. </li></ul><ul><li>The Cretaceous mass extinction that led to the demise of dinosaurs was likely caused by an meteorite hitting the earth. </li></ul>27-
  10. 10. Dinosaurs 27-
  11. 11. Biogeographical Evidence <ul><li>Biogeography is the study of the distribution of plants and animals throughout the world. </li></ul><ul><li>The world’s six biogeographical regions have their own distinct mix of living things. </li></ul><ul><li>Continental drift refers to the changing positions of the continents over time. </li></ul>27-
  12. 12. <ul><li>Two hundred twenty-five million years ago, all the present land masses belonged to one continent (Pangaea). </li></ul><ul><li>The distribution of plants and animals is consistent with continental drift. </li></ul><ul><li>Organisms, such as certain seed plant groups or reptiles, are widely distributed throughout the world. </li></ul><ul><li>Other groups, such as mammals that arose after the continents broke up, have great differences in species on different continents. </li></ul>27-
  13. 13. Continental drift 27-
  14. 14. Anatomical Evidence <ul><li>Despite dissimilar functions, all vertebrate forelimbs contain the same sets of bones – this strongly suggests common descent. </li></ul><ul><li>Structures that are similar because they are inherited from a common ancestor are homologous structures . </li></ul><ul><li>Analogous structures are used for the same purpose but are not due to a common ancestor. </li></ul>27-
  15. 15. Bones of vertebrate forelimbs 27-
  16. 16. <ul><li>Vestigial structures are anatomical features that are fully developed in one group but reduced or nonfunctional in other, similar groups. </li></ul><ul><li>Vestigial structures can be explained by common descent. </li></ul><ul><li>The homology shared by vertebrates extends to their embryological development; all vertebrates have a dorsal notochord and paired pharyngeal pouches at some point. </li></ul><ul><li>Evolution modifies existing structures. </li></ul>27-
  17. 17. Significance of developmental similarities 27-
  18. 18. Biochemical Evidence <ul><li>All organisms have certain biochemicals in common. </li></ul><ul><li>All use DNA, ATP, and many identical or nearly identical enzymes. </li></ul><ul><li>Organisms use the same triplet code and the same 20 amino acids in proteins. </li></ul><ul><li>This similarity is not necessary, but can be explained by common descent. </li></ul>27-
  19. 19. Significance of biochemical differences 27-
  20. 20. Origin of Life <ul><li>Under conditions present on the primitive earth, it is possible that a chemical evolution produced the first cells. </li></ul><ul><li>Chemical evolution refers to the reaction of inorganic chemicals to produce simple organic chemicals, that would later polymerize into macromolecules. </li></ul>27-
  21. 21. <ul><li>Once a plasma membrane formed, a protocell could have come into existence. </li></ul><ul><li>Energy for the chemical reactions could have come from ultraviolet radiation, volcanoes, bombardment by comets, or from oceanic hydrothermal vents. </li></ul><ul><li>The early atmosphere lacked oxygen and also a shield of ozone; it was not until photosynthesis evolved that oxygen was present in earth’s atmosphere. </li></ul>27-
  22. 22. Origin of the first cell(s) 27-
  23. 23. Evolution of Small Organic Molecules <ul><li>Experiments by Stanley Miller in 1953 tested the hypothesis that small organic molecules were formed at the ocean’s surface. </li></ul><ul><li>The first atmospheric gases (methane, ammonia, and hydrogen) were placed into a closed system, heated, and circulated past an electric spark to simulate lightning. </li></ul><ul><li>A variety of amino acids and organic acids formed. </li></ul>27-
  24. 24. Miller’s experiment 27-
  25. 25. Chemical evolution at hydrothermal vents 27-
  26. 26. Macromolecules <ul><li>There are three hypotheses concerning how small organic molecules could give rise to macromolecules: </li></ul><ul><li>The RNA-first hypothesis suggests that only the macromolecule RNA was needed to progress toward the first cell. </li></ul><ul><li>RNA molecules (as ribozymes ) can sometimes be both substrates and enzymes. </li></ul>27-
  27. 27. <ul><li>The protein-first hypothesis , by Sidney Fox, suggested that amino acids collected in small puddles, and heat from the sun caused them to form proteinoids; when proteinoids were returned to water, they formed microspheres and had many properties of cells. </li></ul><ul><li>This hypothesis assumes that DNA came after proteins. </li></ul>27-
  28. 28. <ul><li>The third hypothesis, by Graham Cairns-Smith, suggests that clay was helpful in causing polymerization of both proteins and nucleic acids at the same time. </li></ul><ul><li>Clay attracts small organic molecules and contains iron and zinc, which may have served as inorganic catalysts for polypeptide formation. </li></ul><ul><li>This hypothesis suggests that RNA and polypeptides arose at the same time. </li></ul>27-
  29. 29. The Protocell <ul><li>Before the first true cell, there would have been a protocell that had a lipid-protein membrane and used energy metabolism. </li></ul><ul><li>Fox has shown that if lipids are available to microspheres, the two form a lipid-protein membrane. </li></ul><ul><li>Other work by Alexandr Oparin has shown that concentrated mixtures of macromolecules form coacervate droplets that a semipermeable boundary may form around. </li></ul>27-
  30. 30. Protocell anatomy 27-
  31. 31. The Heterotroph Hypothesis <ul><li>The protocell was likely a heterotroph , absorbing small organic molecules from its environment. </li></ul><ul><li>Natural selection would favor cells able to extract energy from carbohydrates to transform ADP to ATP. </li></ul><ul><li>Fox has shown that microspheres have some catalytic ability, and Oparin found coacervates incorporate available enzymes. </li></ul>27-
  32. 32. The True Cell <ul><li>A true cell is a membrane-bounded structure that can carry on protein synthesis to produce the enzymes that allow DNA to replicate. </li></ul><ul><li>It is possible that the sequence of DNA to RNA to protein developed in stages. </li></ul><ul><li>Once the protocells acquired genes that could replicate, they became cells capable of reproducing, and evolution began. </li></ul>27-
  33. 33. Process of Evolution <ul><li>Individuals do not evolve. </li></ul><ul><li>As evolution occurs, genetic changes occur within a population , and these lead to phenotypic changes that are commonly seen in that population. </li></ul><ul><li>Changes in gene frequencies in populations over time constitute microevolution . </li></ul>27-
  34. 34. Population Genetics <ul><li>A population is all the members of a species occupying a particular area at the same time; members of a population reproduce with each other to produce the next generation. </li></ul><ul><li>The various alleles of all the gene loci in all the members make up the gene pool for the population. </li></ul>27-
  35. 35. <ul><li>Hardy and Weinberg used a binomial expression to calculate the genotypic and phenotypic frequencies of a population: </li></ul><ul><li>p 2 + 2pq + q 2 = 1 </li></ul><ul><li>This expression is used to determine gene frequencies at a given time and to predict gene frequencies in the future. </li></ul><ul><li>If reproduction is completely random, the Hardy-Weinberg equation predicts the same gene pool frequencies generation after generation. </li></ul>27-
  36. 36. Using the Hardy-Weinberg equation 27-
  37. 37. <ul><li>The Hardy-Weinberg Law </li></ul><ul><li>The Hardy-Weinberg law states that gene frequencies will stay the same in a large population over time provided: </li></ul><ul><li>There are no mutations or mutations are balanced. </li></ul><ul><li>There is no genetic drift ; changes in allele frequencies due to chance alone are insignificant. </li></ul><ul><li>There is no gene flow – no migration of individuals in or out of the population. </li></ul>27-
  38. 38. <ul><li>Mating is random – individuals pair by chance and not by choice. </li></ul><ul><li>There is no selection – no selective force favors one genotype over another. </li></ul><ul><li>In real life, these conditions are rarely met, and microevolution, as seen by changing gene frequencies in Hardy-Weinberg equilibrium, occurs. </li></ul>27-
  39. 39. Microevolution 27-
  40. 40. Five Agents of Evolutionary Change <ul><li>Mutations </li></ul><ul><li>Mutations provide new alleles and therefore underlie all other mechanisms that produce variation. </li></ul><ul><li>Mutations alone are unlikely to cause evolution; selective agents acting on heritable variation cause evolution. </li></ul><ul><li>The adaptive value of a mutation depends on the environmental conditions. </li></ul>27-
  41. 41. <ul><li>Genetic Drift </li></ul><ul><li>Genetic drift refers to changes in allele frequencies of a gene pool due to chance; genetic drift has a much larger effect in a small population. </li></ul><ul><li>The founder effect occurs when a few individuals leave the original population and begin a new population. </li></ul><ul><li>A bottleneck effect is seen when much of a population is killed due to a natural disaster, and only a few remaining individuals are left to begin a new population. </li></ul>27-
  42. 42. Genetic drift 27-
  43. 43. Founder effect 27-
  44. 44. <ul><li>Gene Flow </li></ul><ul><li>Gene flow is the movement of alleles between populations, such as when individuals migrate from one population to another. </li></ul><ul><li>Gene flow between two populations keeps their gene pools similar and prevents close adaptation to a local environment. </li></ul>27-
  45. 45. <ul><li>Nonrandom Mating </li></ul><ul><li>Nonrandom mating occurs when individuals pair up, not by chance, but according to genotypes and phenotypes. </li></ul><ul><li>Inbreeding is an example of nonrandom mating. </li></ul><ul><li>In a human population, inbreeding increases the frequency of recessive abnormalities. </li></ul>27-
  46. 46. <ul><li>Natural Selection </li></ul><ul><li>Natural selection is the process by which populations become adapted to their environment. </li></ul><ul><li>Evolution by natural selection requires: </li></ul><ul><li>Variation </li></ul><ul><li>Inheritance of the genetic difference </li></ul><ul><li>Differential adaptedness </li></ul><ul><li>Differential reproduction. </li></ul>27-
  47. 47. <ul><li>Three types of natural selection are known: </li></ul><ul><li>Stabilizing selection – an intermediate phenotype is favored. </li></ul><ul><li>Directional selection – one extreme phenotype is favored. </li></ul><ul><li>Disruptive selection – both extreme phenotypes are favored over an intermediate phenotype. </li></ul>27-
  48. 48. Stabilizing selection 27-
  49. 49. Directional selection 27-
  50. 50. Disruptive selection 27-
  51. 51. Maintenance of Variation <ul><li>An example of sickle-cell disease shows how genetic variation is sometimes maintained within a population. </li></ul><ul><li>Persons with sickle cell disease have sickle-shaped blood cells, which can lead to hemorrhage and death. </li></ul><ul><li>Persons without a sickle-cell gene are susceptible to malaria in parts of Africa. </li></ul><ul><li>But heterozygotes, with one sickle-cell gene and one normal gene, have only minor problems with blood cells and are resistant to malaria. </li></ul>27-
  52. 52. Speciation <ul><li>A species is a group of interbreeding subpopulations that share a gene pool and are isolated reproductively from other species. </li></ul><ul><li>Reproductive isolation can occur due to premating isolating mechanisms , in which reproduction is not attempted, or postmating isolating mechanisms that do not produce fertile offspring. </li></ul>27-
  53. 53. Process of Speciation <ul><li>Whenever reproductive isolation develops, speciation has occurred. </li></ul><ul><li>Allopatric speciation occurs when a geographic barrier isolates two subpopulations from each other; when the barrier is removed, the two groups are no longer able to reproduce. </li></ul><ul><li>Sympatric speciation occurs when a single population suddenly becomes two reproductively isolated groups without geographic separation. </li></ul>27-
  54. 54. Allopatric speciation 27-
  55. 55. Adaptive Radiation <ul><li>The evolution of several species of finches on the Galapagos Islands is an example of adaptive radiation because each one has a different way of life. </li></ul><ul><li>Adaptive radiation occurs when a few individuals migrate to a new area, then natural selection promotes different feeding habits in different ecological habitats. </li></ul>27-
  56. 56. The Galapagos finches 27-
  57. 57. The Pace of Speciation <ul><li>Two hypotheses concern the pace of speciation: </li></ul><ul><li>Phyletic gradualism – suggests that change is slow and steady within a lineage before and after a divergence; few transitional links would exist. </li></ul><ul><li>Punctuated equilibrium – suggests that a period of no change is punctuated by period of rapid speciation. </li></ul>27-
  58. 58. Phyletic gradualism versus punctuated equilibrium 27-
  59. 59. Classification <ul><li>Classification involves the assignment of species to a hierarchy of categories: species, genus, family, order, class, phylum, kingdom, and domain. </li></ul><ul><li>Each species has a binomial scientific name including the genus and species. </li></ul><ul><li>Humans are Homo sapiens . </li></ul>27-
  60. 60. Five-Kingdom System <ul><li>The five-kingdom system of classification is based on structural differences and also on modes of nutrition among the eukaryotes. </li></ul><ul><li>The five kingdoms include: </li></ul><ul><li>Monera (prokaryotes) </li></ul><ul><li>Eukaryotic kingdoms of Protista, Fungi, Plantae, and Animalia. </li></ul>27-
  61. 61. Five-kingdom system of classification 27-
  62. 62. Three-Domain System <ul><li>The three-domain system recognizes three domains: Bacteria, Archaea, and Eukarya. </li></ul><ul><li>This system of classification is based on biochemical differences that show there are three vastly different groups of organisms. </li></ul>27-
  63. 63. Three-domain system of classification 27-
  64. 64. The three domains of life 27-
  65. 65. Chapter Summary <ul><li>The fossil record and biogeography, as well as comparative anatomy, development, and biochemistry all give evidence for evolution. </li></ul><ul><li>All organisms have certain biochemicals in common, and chemical similarities indicate the degree of relatedness. </li></ul><ul><li>The fossil record shows that mass extinctions occurred several times. </li></ul>27-
  66. 66. <ul><li>Chemical evolution likely resulted in the first cells. </li></ul><ul><li>Inorganic chemicals derived from the primitive atmosphere reacted to form simple organic molecules. </li></ul><ul><li>The RNA-first and protein-first hypotheses seek to explain how the first protocell arose. </li></ul><ul><li>Eventually, the DNA -> RNA -> protein self-replicating system evolved, as did the first true cell. </li></ul>27-
  67. 67. <ul><li>Evolution is a process that involves changes in gene frequencies in a population according to Hardy-Weinberg equilibrium. </li></ul><ul><li>Equilibrium is maintained unless disrupted by mutations, genetic drift, gene flow, nonrandom mating, or natural selection. </li></ul><ul><li>Speciation requires geographic isolation followed by reproductive isolation. </li></ul>27-
  68. 68. <ul><li>There are two hypotheses regarding the pace of evolution – phyletic gradualism and punctuated equilibrium. </li></ul><ul><li>Classification involves the assignment of species to a hierarchy of categories: species, genus, family, order, class, phylum, kingdom, and domain. </li></ul><ul><li>The three-domain system recognizes three domains: Bacteria, Archaea, and Eukarya. </li></ul>27-

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