1.3

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