Transcript A game of selection powerpoint

A Game of Selection:
…You Win or You Die!!!
Evolution: What does it mean???
Evolution: How do we define it?
• Change in avg phenotype over time
Evolution: How do we define it?
• Change in avg phenotype over time
• Change in allele frequency over time
Mechanisms of evolution?
Mechanisms of evolution?
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Genetic drift
Biased mutations
Gene flow
Natural selection
Natural selection
• Gradual nonrandom process by which biological
traits become more/less common in a population
due to differential reproduction
Three components of natural selection
• Variation – traits are variable within populations
• Selection – traits affect fitness (ability to survive and
reproduce)
• Heredity – traits are heritable across generations
Variation
Fitness (# offspring)
Selection
Light ---------------------> Dark
Coloration
Heredity
Three components of natural selection
• Variation
• Selection
• Heredity
When these components are all
present you will have evolution
by natural selection!
Types of selection
• Directional
• Stabilizing
• Disruptive
Directional
• Species of mouse that lives among dark rocks where dark fur conceals
them from predators…what is going to happen to the population over
time?
Directional
• Species of mouse that lives among dark rocks where dark fur conceals
them from predators…what is going to happen to the population over
time?
Stabilizing
• If the species of mouse lives in an area with rocks of intermediate color
what do you think is going to happen to the population over time?
Stabilizing
• If the species of mouse lives in an area with rocks of intermediate color
what do you think is going to happen to the population over time?
Disruptive
• Sticking with the mouse example, imagine the species lives in an area
made up of patches of light colored rocks and patches of dark colored
rocks….what do you think will happen to the population over time?
Disruptive
• Sticking with the mouse example, imagine the species lives in an area
made up of patches of light colored rocks and patches of dark colored
rocks….what do you think will happen to the population over time?
Important to keep in mind!
• Selection can only act on existing variation
Here is a population of bacteria with
individuals varying in their degree of
antibiotic resistance. What will happen when
antibiotic is added?
No resistance -------------------> High resistance
Important to keep in mind!
• Selection can only act on existing variation
Antibiotics added
Antibiotic resistance was
already present in the
population, it does not arise in
response to the antibiotic.
No resistance -------------------> High resistance
Important to keep in mind!
• Selection can only act on existing variation
Antibiotics added
Final population
No resistance -------------------> High resistance
Important to keep in mind!
• Individuals are selected but populations evolve
A population of cute furry rabbits have recently migrated into a new
environment that is much colder than their home range. Having thicker fur
provides a large advantage in this new environment. When the rabbits first
arrive their population consists of individuals with a wide range of fur
thickness.
This is Bob. Bob is a rabbit with a pretty thin coat of fur. Will Bob be able to
adapt to the new environment?
Important to keep in mind!
• Individuals are selected but populations evolve
No. Bob and others like him will die off while those with thick fur survive
and reproduce so that over time the population average fur thickness
increases. Individuals cannot evolve themselves, populations evolve.
Now its time for a game!