1.3

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1.3

  1. 1. AIM: How can natural selection be observed? Warm – up: Describe one piece of evidence that supports evolution
  2. 2. Selection Pressures • What type of environmental resistances exist to keep populations stable?
  3. 3. Selection: Advantages & Disadvantages
  4. 4. Selection: Advantages & Disadvantages • Organisms with characteristics that aid in their survival have a selective advantage and therefore have high natality
  5. 5. Selection: Advantages & Disadvantages • Organisms with characteristics that aid in their survival have a selective advantage and therefore have high natality • Organisms with unfavorable characteristics are at a selective disadvantage and therefore have high mortality
  6. 6. Fitness Body size & egg laying in water striders • Ability of an organism to pass on its alleles to subsequent generations, compared with individuals of the same species
  7. 7. Fitness Body size & egg laying in water striders • Ability of an organism to pass on its alleles to subsequent generations, compared with individuals of the same species
  8. 8. Fitness Body size & egg laying in water striders • Ability of an organism to pass on its alleles to subsequent generations, compared with individuals of the same species
  9. 9. Fitness Body size & egg laying in water striders • Ability of an organism to pass on its alleles to subsequent generations, compared with individuals of the same species
  10. 10. Types of Natural Selection
  11. 11. Types of Natural Selection • The frequency of an allele in a population typically has a normal distribution
  12. 12. Types of Natural Selection • The frequency of an allele in a population typically has a normal distribution • Natural selection affects a gene pool (all the alleles and genes in a population) by increasing the frequency of advantageous alleles and decreasing the frequency of disadvantageous alleles.
  13. 13. Stabilizing Selection In an unchanging environment, the extreme variations are selected against and the intermediate characteristics have a selective advantage.
  14. 14. Directional Selection Favors one extreme of the phenotype and results in a shift of the mean phenotype. Generally follows some type of environmental change.
  15. 15. Directional Selection Favors one extreme of the phenotype and results in a shift of the mean phenotype. Generally follows some type of environmental change.
  16. 16. Disruptive Selection Favors the extreme phenotypes and selects against intermediates. Leads to a bimodal distribution. What happens if the two groups are unable to interbreed?
  17. 17. Individuals DON’T evolve…
  18. 18. Individuals DON’Tdon’t survive… Individuals survive or evolve…
  19. 19. Individuals are selected
  20. 20. Individuals are selected Populations evolve
  21. 21. Variation & natural selection
  22. 22. Variation & natural selection • Variation is the raw material for natural selection
  23. 23. Variation & natural selection • Variation is the raw material for natural selection – there have to be differences within population
  24. 24. Variation & natural selection • Variation is the raw material for natural selection – there have to be differences within population – some individuals must be more fit than others
  25. 25. Where does Variation come from? Wet year Beak depth Dry year Dry year Dry year 1977 1980 1982 1984 11 offspring (mm) Beak depth of 10 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  26. 26. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year 1977 1980 1982 1984 11 offspring (mm) Beak depth of 10 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  27. 27. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 11 offspring (mm) Beak depth of 10 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  28. 28. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 offspring (mm) Beak depth of 10 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  29. 29. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  30. 30. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 Medium ground finch 8 8 9 10 11 Mean beak depth of parents (mm)
  31. 31. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 Mean beak depth of parents (mm)
  32. 32. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 • recombination of alleles Mean beak depth of parents (mm)
  33. 33. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 • recombination of alleles Mean beak depth of parents (mm) – new arrangements in every offspring
  34. 34. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 • recombination of alleles Mean beak depth of parents (mm) – new arrangements in every offspring • new combinations = new phenotypes
  35. 35. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 • recombination of alleles Mean beak depth of parents (mm) – new arrangements in every offspring • new combinations = new phenotypes – spreads variation
  36. 36. Where does Variation come from? Wet year Beak depth • Mutation Dry year Dry year Dry year – random changes to DNA 1977 1980 1982 1984 • errors in mitosis & meiosis 11 • environmental damage offspring (mm) Beak depth of 10 • Sex 9 – mixing of alleles 8 Medium ground finch 8 9 10 11 • recombination of alleles Mean beak depth of parents (mm) – new arrangements in every offspring • new combinations = new phenotypes – spreads variation • offspring inherit traits from parent
  37. 37. Mutation & Variation
  38. 38. Mutation & Variation
  39. 39. Mutation & Variation • Mutation creates variation
  40. 40. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing
  41. 41. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence
  42. 42. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence – changes amino acid sequence?
  43. 43. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence – changes amino acid sequence? – changes protein?
  44. 44. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence – changes amino acid sequence? – changes protein? • changes structure?
  45. 45. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence – changes amino acid sequence? – changes protein? • changes structure? • changes function?
  46. 46. Mutation & Variation • Mutation creates variation – new mutations are constantly appearing • Mutation changes DNA sequence – changes amino acid sequence? – changes protein? • changes structure? • changes function? – changes in protein may change phenotype & therefore change fitness
  47. 47. Antibiotic Resistance
  48. 48. Antibiotic Resistance
  49. 49. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them.
  50. 50. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them.
  51. 51. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them. Process:
  52. 52. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them. Process: - A mutation produces an individual bacterium with an allele that allows it to produce an enzyme that deactivates the enzyme or that reduces the number of target receptors on the membrane.
  53. 53. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them. Process: - A mutation produces an individual bacterium with an allele that allows it to produce an enzyme that deactivates the enzyme or that reduces the number of target receptors on the membrane. - The bacteria becomes resistant and therefore will survive and reproduce other antibiotic resistant bacteria.
  54. 54. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them. Process: - A mutation produces an individual bacterium with an allele that allows it to produce an enzyme that deactivates the enzyme or that reduces the number of target receptors on the membrane. - The bacteria becomes resistant and therefore will survive and reproduce other antibiotic resistant bacteria. - The antibiotic applies a selection pressure
  55. 55. Antibiotic Resistance • Due to overuse of antibiotics, many strains of bacteria have developed resistance to them. Process: - A mutation produces an individual bacterium with an allele that allows it to produce an enzyme that deactivates the enzyme or that reduces the number of target receptors on the membrane. - The bacteria becomes resistant and therefore will survive and reproduce other antibiotic resistant bacteria. - The antibiotic applies a selection pressure
  56. 56. DDT Resistance in Anopheline Mosquitoes
  57. 57. The malarial parasite is spread by anopheline mosquitoes
  58. 58. The malarial parasite is spread by anopheline mosquitoes The spread of malaria can be controlled by controlling mosquito numbers
  59. 59. The malarial parasite is spread by anopheline mosquitoes The spread of malaria can be controlled by controlling mosquito numbers One way of controlling mosquito numbers is to use an insecticide like DDT DDT
  60. 60. Not every mosquito will be killed each time we spray
  61. 61. Not every mosquito will be killed each time we spray
  62. 62. Not every mosquito will be killed each time we spray Some will survive to repopulate the area, so…
  63. 63. Not every mosquito will be killed each time we spray Some will survive to repopulate the area, so… …we must spray frequently.
  64. 64. Random mutation may produce mosquitoes which are resistant to the effects of DDT…
  65. 65. Random mutation may produce mosquitoes which are resistant to the effects of DDT…
  66. 66. Random mutation may produce mosquitoes which are resistant to the effects of DDT… …these are more likely to survive and pass on their genes to the next generation
  67. 67. NOTE
  68. 68. NOTE A resistant mosquito does not need to be totally resistant to the effects of DDT…
  69. 69. NOTE A resistant mosquito does not need to be totally resistant to the effects of DDT… … it may just be able to survive higher does of DDT than ‘normal’ mosquitoes.
  70. 70. The next generation contains more resistant mosquitoes
  71. 71. The next generation contains more resistant mosquitoes
  72. 72. The next generation contains more resistant mosquitoes Again, they are more likely to survive to reproduce, so…
  73. 73. The next generation contains more resistant mosquitoes Again, they are more likely to survive to reproduce, so… …the proportion of the population which is resistant to DDT increases
  74. 74. With each successive generation…
  75. 75. With each successive generation… …the proportion of the mosquito population which is resistant to DDT increases.
  76. 76. Eventually…
  77. 77. Eventually… …the whole population may consist of resistant mosquitoes
  78. 78. Spraying with DDT produces the selective pressure which favours the resistant mosquitoes.
  79. 79. Spraying with DDT produces the selective pressure which favours the resistant mosquitoes. Because they can resist the effects of DDT, the resistant mosquitoes are said to have a selective advantage
  80. 80. It may not be able to increase the dose of DDT used:
  81. 81. It may not be able to increase the dose of DDT used: - higher doses may be dangerous to humans
  82. 82. It may not be able to increase the dose of DDT used: - higher doses may be dangerous to humans - higher doses may be too damaging to other wildlife
  83. 83. It may not be able to increase the dose of DDT used: - higher doses may be dangerous to humans - higher doses may be too damaging to other wildlife Using higher doses of DDT will also produce the selective pressure which will favour mosquitoes with even higher levels of resistance
  84. 84. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed
  85. 85. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed
  86. 86. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed
  87. 87. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed
  88. 88. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed Year % dark % light
  89. 89. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed Year % dark % light 1848 5 95
  90. 90. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed Year % dark % light 1848 5 95 1895 98 2
  91. 91. Peppered Moths • Dark vs. light variants • Polymorphism: two or more adult body forms contained within a single species and can interbreed Year % dark % light 1848 5 95 1895 98 2 1995 19 81
  92. 92. Peppered Moths
  93. 93. Peppered Moths • What was the selection factor?
  94. 94. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England
  95. 95. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution
  96. 96. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution
  97. 97. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark
  98. 98. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England
  99. 99. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees
  100. 100. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark
  101. 101. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark – mid 1900s = pollution controls
  102. 102. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark – mid 1900s = pollution controls • clean air laws
  103. 103. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark – mid 1900s = pollution controls • clean air laws • return of lichen = light colored bark
  104. 104. Peppered Moths • What was the selection factor? – early 1800s = pre-industrial England • low pollution • lichen growing on trees = light colored bark – late 1800s = industrial England • factories = soot coated trees • killed lichen = dark colored bark – mid 1900s = pollution controls • clean air laws • return of lichen = light colored bark – industrial melanism

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