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AIM: How can natural selection be
observed?
Warm – up:
Describe one piece of evidence that supports evolution
Selection Pressures
• What type of environmental resistances exist to keep populations stable?
Selection: Advantages & Disadvantages
Selection: Advantages & Disadvantages
• Organisms with characteristics that aid in their survival have a selective advantage and therefore have high natality
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
Fitness• Ability of an organism to
pass on its alleles to subsequent generations, compared with individuals of the same species
Body size & egg laying in water striders
Fitness• Ability of an organism to
pass on its alleles to subsequent generations, compared with individuals of the same species
Body size & egg laying in water striders
Fitness• Ability of an organism to
pass on its alleles to subsequent generations, compared with individuals of the same species
Body size & egg laying in water striders
Fitness• Ability of an organism to
pass on its alleles to subsequent generations, compared with individuals of the same species
Body size & egg laying in water striders
Types of Natural Selection
Types of Natural Selection
• The frequency of an allele in a population typically has a normal distribution
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.
Stabilizing Selection
In an unchanging environment, the extreme variations are selected against and the intermediate characteristics have a
selective advantage.
Directional Selection
Favors one extreme of the phenotype and results in a shift of the mean phenotype. Generally follows some type of
environmental change.
Directional Selection
Favors one extreme of the phenotype and results in a shift of the mean phenotype. Generally follows some type of
environmental change.
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?
Individuals DON’T evolve…
Individuals DON’T evolve…Individuals survive or don’t survive…
Individuals are selected
Populations evolve
Individuals are selected
Variation & natural selection
Variation & natural selection • Variation is the raw material for natural
selection
Variation & natural selection • Variation is the raw material for natural
selection– there have to be differences within population
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
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
• recombination of alleles
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
• recombination of alleles– new arrangements in every offspring
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
• recombination of alleles– new arrangements in every offspring
• new combinations = new phenotypes
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
• recombination of alleles– new arrangements in every offspring
• new combinations = new phenotypes
– spreads variation
Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry year
Dry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from?
• Mutation– random changes to DNA
• errors in mitosis & meiosis• environmental damage
• Sex – mixing of alleles
• recombination of alleles– new arrangements in every offspring
• new combinations = new phenotypes
– spreads variation• offspring inherit traits from parent
Mutation & Variation
Mutation & Variation
Mutation & Variation • Mutation creates variation
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
• Mutation changes DNA sequence
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
• Mutation changes DNA sequence– changes amino acid sequence?
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
• Mutation changes DNA sequence– changes amino acid sequence?– changes protein?
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
• Mutation changes DNA sequence– changes amino acid sequence?– changes protein?
• changes structure?
Mutation & Variation • Mutation creates variation
– new mutations are constantly appearing
• Mutation changes DNA sequence– changes amino acid sequence?– changes protein?
• changes structure?
• changes function?
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
Antibiotic Resistance
Antibiotic Resistance
Antibiotic Resistance
• Due to overuse of antibiotics, many strains of bacteria have developed resistance to them.
Antibiotic Resistance
• Due to overuse of antibiotics, many strains of bacteria have developed resistance to them.
Antibiotic Resistance
• Due to overuse of antibiotics, many strains of bacteria have developed resistance to them.
Process:
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.
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.
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
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
DDT Resistance in Anopheline Mosquitoes
The malarial parasite is spread by anopheline mosquitoes
The malarial parasite is spread by anopheline mosquitoes
The spread of malaria can be controlled by controlling mosquito numbers
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
Not every mosquito will be killed each time we spray
Not every mosquito will be killed each time we spray
Not every mosquito will be killed each time we spray
Some will survive to repopulate the area, so…
Not every mosquito will be killed each time we spray
Some will survive to repopulate the area, so… …we must spray frequently.
Random mutation may produce mosquitoes which are resistant to the effects of DDT…
Random mutation may produce mosquitoes which are resistant to the effects of DDT…
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
NOTE
NOTE
A resistant mosquito does not need to be totally resistant to the effects of DDT…
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.
The next generation contains more resistant mosquitoes
The next generation contains more resistant mosquitoes
The next generation contains more resistant mosquitoes
Again, they are more likely to survive to reproduce, so…
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
With each successive generation…
With each successive generation…
…the proportion of the mosquito population which is resistant to DDT increases.
Eventually…
Eventually…
…the whole population may consist of resistant mosquitoes
Spraying with DDT produces the selective pressure which favours the resistant mosquitoes.
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
It may not be able to increase the dose of DDT used:
It may not be able to increase the dose of DDT used:
- higher doses may be dangerous to humans
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
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
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Year % dark % light
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Year % dark % light1848 5 95
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Year % dark % light1848 5 951895 98 2
Peppered Moths• Dark vs. light variants• Polymorphism: two or more adult body forms contained
within a single species and can interbreed
Year % dark % light1848 5 951895 98 21995 19 81
Peppered Moths
Peppered Moths• What was the selection factor?
Peppered Moths• What was the selection factor?
– early 1800s = pre-industrial England
Peppered Moths• What was the selection factor?
– early 1800s = pre-industrial England• low pollution
Peppered Moths• What was the selection factor?
– early 1800s = pre-industrial England• low pollution
Peppered Moths• What was the selection factor?
– early 1800s = pre-industrial England• low pollution
• lichen growing on trees = light colored bark
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
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
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
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
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
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
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
