4. Selection:
Advantages & Disadvantages
• Organisms with characteristics that aid in
their survival have a selective advantage
and therefore have high natality
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. 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. 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. 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. 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
11. Types of Natural Selection
• The frequency of an allele in a population
typically has a normal distribution
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. Stabilizing Selection
In an unchanging environment, the extreme variations are
selected against and the intermediate characteristics have a
selective advantage.
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. 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. 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?
22. Variation & natural selection
• Variation is the raw material for natural
selection
23. Variation & natural selection
• Variation is the raw material for natural
selection
– there have to be differences within population
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
49. Antibiotic Resistance
• Due to overuse of antibiotics, many strains of
bacteria have developed resistance to them.
50. Antibiotic Resistance
• Due to overuse of antibiotics, many strains of
bacteria have developed resistance to them.
51. Antibiotic Resistance
• Due to overuse of antibiotics, many strains of
bacteria have developed resistance to them.
Process:
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. 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. 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. 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
58. The malarial parasite is spread by
anopheline mosquitoes
The spread of malaria can
be controlled by
controlling mosquito
numbers
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
62. Not every mosquito will be killed each time
we spray
Some will survive to repopulate the area, so…
63. Not every mosquito will be killed each time
we spray
Some will survive to repopulate the area, so…
…we must spray frequently.
64. Random mutation may produce mosquitoes which are
resistant to the effects of DDT…
65. Random mutation may produce mosquitoes which are
resistant to the effects of DDT…
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
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.
72. The next generation contains more resistant
mosquitoes
Again, they are more likely to survive to reproduce, so…
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
79. Spraying with DDT produces the
selective pressure which favours
the resistant mosquitoes.
80. 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
81. It may not be able to increase the
dose of DDT used:
82. It may not be able to increase the
dose of DDT used:
- higher doses may be dangerous
to humans
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
84. 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
85. Peppered Moths
• Dark vs. light variants
• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
86. Peppered Moths
• Dark vs. light variants
• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
87. Peppered Moths
• Dark vs. light variants
• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
88. Peppered Moths
• Dark vs. light variants
• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
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
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
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
92. 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
95. Peppered Moths
• What was the selection factor?
– early 1800s = pre-industrial England
96. Peppered Moths
• What was the selection factor?
– early 1800s = pre-industrial England
• low pollution
97. Peppered Moths
• What was the selection factor?
– early 1800s = pre-industrial England
• low pollution
98. Peppered Moths
• What was the selection factor?
– early 1800s = pre-industrial England
• low pollution
• lichen growing on trees = light colored bark
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
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
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
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
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
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
105. 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
