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Chapter 3

BIO220H1 Chapter Notes - Chapter 3: Serial Dilution, Uracil, Flocculation

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John Stinchcombe

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BIO220 H1-S Lab Notes
Chapter 3: Cooperation in Yeast
Inclusive Fitness
- Two strategies for gene to be favoured by natural selection
1. Gene increases fitness of individual it’s in (direct fitness)
2. Increases fitness of other individuals that carry copies of the gene (indirect
oStrategy 2 might come at a cost to individual fitness
oEX: worker bees help queen of hive to reproduce but they don’t reproduce
Costly to direct fitness
But have indirect fitness since they’re related to queen/share her genes
- If indirect fitness benefits outweigh cost of direct fitness, may have costly cooperative
oi.e. sterile worker ant
oIndividual might try to maximize inclusive fitness [indirect + direct fitness
Kin selection and Greenbeards
- Two ways to increase indirect fitness effects
1. Direct costly cooperative behaviour to kin
oResults in kin selection
oIf died by saved kin, then still passing genes to next generation
2. Direct costly cooperative behaviour to individuals that not might be kin but have
phenotypic label that means have same gene
o= relatedness at locus for social behaviour (not average relatedness)
oIndividuals may share gene that:
Creates noticeable phenotypic label
Allows individual with label to ID other individuals w/ same label
Cause individual w/ same label to behave favourable to other individual
w/ label
Maybe person with greenbeard cooperates with others greenbearded
Gene that provides mechanism for costly cooperative behaviour to evolve
even though they not kin
Doesn’t necessarily have noticeable phenotypic label
Cooperation in Microorganisms
- Microbes also have social behaviours
- Yeast usually unicellular
- Sometimes clumps with thousands of others making ‘flocs’
oFlocculation behaviour controlled by single locus polymorphism
Polymorphism: 2 phenotypes –one that floc and don’t floc
Depends on genotype at a single locus
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