genetic variation - the fuel of natural selection campbell et al, chapter 23
TRANSCRIPT
![Page 1: Genetic Variation - The fuel of natural selection Campbell et al, chapter 23](https://reader035.vdocuments.us/reader035/viewer/2022070305/5515cb19550346c6278b47d6/html5/thumbnails/1.jpg)
Genetic Variation -The fuel of natural selection
Campbell et al, chapter 23
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• Populations are polymorphic
• Nature vs. Nurture
• Source of variation
• Maintenance of variation
![Page 3: Genetic Variation - The fuel of natural selection Campbell et al, chapter 23](https://reader035.vdocuments.us/reader035/viewer/2022070305/5515cb19550346c6278b47d6/html5/thumbnails/3.jpg)
• Populations are polymorphic
• Nature vs. Nurture
• Source of variation
• Maintenance of variation
![Page 4: Genetic Variation - The fuel of natural selection Campbell et al, chapter 23](https://reader035.vdocuments.us/reader035/viewer/2022070305/5515cb19550346c6278b47d6/html5/thumbnails/4.jpg)
Polymorphic populations
Example: Darwin finches on Galapagos
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Polymorphic populations
Example: Lazuli bunting
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Polymorphic populations
Example: Swallowtail butterfly
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• Populations are polymorphic
• Nature vs. Nurture
• Source of variation
• Maintenance of variation
![Page 8: Genetic Variation - The fuel of natural selection Campbell et al, chapter 23](https://reader035.vdocuments.us/reader035/viewer/2022070305/5515cb19550346c6278b47d6/html5/thumbnails/8.jpg)
Nature vs. Nurture
PhenotypicExpression
Protein
Genome(blueprint)
Nature
Environment
Nurture
I found the gene that makes us believe alltraits are based on genes
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Nature vs. Nurture
GeneChromosome
Genome
Genepool
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Nature vs. Nurture
Diploidy
There are 2 copies of each gene
Father Mother
Offspring
2 identical copies = homozygot
Father Mother
Offspring
2 different copies = heterozygot
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Nature vs. Nurture
• Genotype is more variable than phenotype
• Only genetic variation counts for evolution
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Nature vs. Nurture
How to separate the two?
Example: Altitudinal gradient Common Garden Exp.
Gene
Environment
Mixture of both
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• Populations are polymorphic
• Nature vs. Nurture
• Source of variation Mutation Recombination
• Maintenance of variation
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Source of Genetic Variation
1. Mutation
Change in: DNA sequence
Chromosome structure
Number of Chromosomes
Due to: Copying Errors
Environmental factors
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Source of Genetic Variation
2. Recombination
• Reshuffling of chromosomes during reproduction
• Crossing over
A
B
C
A
B
C
A
B
C
A
B
C
![Page 16: Genetic Variation - The fuel of natural selection Campbell et al, chapter 23](https://reader035.vdocuments.us/reader035/viewer/2022070305/5515cb19550346c6278b47d6/html5/thumbnails/16.jpg)
• Populations are polymorphic
• Nature vs. Nurture
• Source of variation
• Maintenance of variation Selection Heterosis
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Maintenance of Variation
1. Stabilising selection
Favours mean over tail
Loss of variation
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Maintenance of Variation
1. Stabilising selection
Example: Darwin Finches
Bill size
For
agin
g ef
ficie
ncy
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Maintenance of Variation
2. Directional selection
One tail is favoured overthe other
Trait is changing over time
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Maintenance of Variation
2. Directional selection
Example: Heliconius butterfly on passion flower vines
Plant:Toxin
Insect:Enzymes
Plant:False eggs
Leads to an arms race between plant and insect
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Maintenance of Variation
2. Directional selection
The arms race idea lead to a more general hypothesis:Red Queen Hypothesis
‘It takes you all the running to stay in place’
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Maintenance of Variation
2. Directional selection
Selection may change in timeExample: Darwin Finches on Galapagos
Time
Bill
siz
e
El Nino
wet drysmall large seeds
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Maintenance of Variation
2. Directional selection
Selection may change in spaceExample: African Firefinches
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Maintenance of Variation
3. Disruptive selection
Selection favours the two tails over the mean
There are two forms
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Maintenance of Variation
3. Disruptive selectionExample: Lazuli buntings
Showy male
Average male
Drabmale
attracted Sneak in
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Maintenance of Variation
4. Frequency-dependent selection
A mode of selection where a phenotype is onlyfavoured when it is either rare or common.
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Maintenance of Variation
4. Frequency-dependent selection
Example: Swallowtail butterfly (Papillo dardanus)
Males
Toxic species
Only works if the cheats are rare
Swallowtail females mimicthese toxic species without being toxic themselves
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Maintenance of Variation
5. Heterozygote advantage
Heterozygote individuals have higher fitness than eitherhomozygote individuals.
This is a common principle in plant and animal breeding
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Maintenance of Variation
5. Heterozygote advantage
Example: Red blood cells - sickle cell disease
Homozygot (normal cells): vulnerable to malaria
Homozygote (sickled cells): lethal
Heterozygote: non-lethal & resistant to malaria
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A large number of processescreate and maintain geneticvariation that is the base forevolution...
…but does this lead tonew species? - next here