Patterns of Evolution
Essential Questions:
1. What are the mechanisms that lead to
evolutionary change over time?
2. How do different species evolve?
3. Does evolutionary change occur in our lifetime?
A. Mechanisms of Change
I. Genetic Variation
1. Mutations
2. Sex  Gene shuffling
II. Gene Flow (Migration)
III. Genetic Drift
1. Bottleneck Effect
2. Founder Effect
IV. Natural Selection
1. Stabilizing Selection
2. Directional Selection
3. Stabilizing Selection
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I. Genetic Variation
How might variation
occur in a single
population?
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I. Genetic Variation
1. Mutations
2. Sex  Gene shuffling
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I. Genetic Variation
1. Mutations
Mutation: A change in our DNA sequence
• Some mutations are not inherited
(do not get passed on)
Example: color of an
individual apple
• Some mutations are inherited (do get passed on)
Example: Lice, Sickle cell anemia
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I. Genetic Variation
1. Mutations
Example: Lice
The louse that has
a mutation that
makes it resistant
to the lice-killing
shampoo can
produce offspring
that also have that
mutation
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I. Genetic Variation
1. Mutations
Example: Lice
Example: sickle cell anemia
The louse that has
a mutation that
makes it resistant
to the lice-killing
shampoo can
produce offspring
that also have that
mutation
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I. Genetic Variation
2. Sex (gene shuffling)
How did this young wildebeest get so much
variation in her DNA?
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A herd of wildebeests?
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A herd of DNA (the genetic information that makes
us who we are, and wildebeests who they are)!
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Sex is an elaborate
way to maintain
genetic diversity
in a population by
shuffling our genetic
information around!
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How can genetic variation occur
between different populations?
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How can genetic variation occur
between different populations?
What happens when the wind blows
the pollen off of these oak catkins?
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II. Gene Flow (Migration)
Gene flow: any movement of genes (genetic info)
from one population to another
How might gene flow happen?
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II. Gene Flow (Migration)
Gene flow: any movement of genes (genetic info)
from one population to another
How might gene flow happen?
Examples: Corn, milkweed
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Is there such thing as luck in evolution?
Does anything happen by chance?
Do the “best fit” always survive?
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Is there such thing as luck in evolution?
Does anything happen by chance?
Do the “best fit” always survive?
What if the seed of a “fit” plant is eaten by a bird, but then
pooped out in a parking lot instead of fertile soil? Will
that “fit” plant successfully reproduce?
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III. Genetic Drift
Genetic drift: individuals in a population survive and
reproduce due to random chance,
NOT because they are more “fit,” as in
natural selection.
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III. Genetic Drift
Genetic drift: individuals in a population survive and
reproduce due to random chance,
NOT because they are more “fit,” as in
natural selection.
• Genetic drift decreases diversity within a population
• Genetic drift impacts the diversity of small populations
• Genetic drift can create a “bottleneck effect” or
“founder effect”
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III. Genetic Drift
1. Bottleneck Effect
Bottleneck effect: A random event dramatically
decreases the population size (and, therefore,
genetic diversity) for at least one generation.
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III. Genetic Drift
1. Bottleneck Effect
Bottleneck effect: A random event dramatically
decreases the population size (and, therefore,
genetic diversity) for at least one generation.
Examples: Northern elephant seals, Cheetahs
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What if the few individuals that colonized a new
habitat carried DNA that only coded for
proteins that produced blonde hair?
What would the future population look like?
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What if the few individuals that colonized a new
habitat carried DNA that only coded for
proteins that produced blonde hair?
What would the future population look like?
What if the few individuals that colonized a new
habitat carried a mutation in their DNA that
caused a disorder or disease?
What would the future population be like?
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III. Genetic Drift
2. Founder Effect
Founder effect: a few members of an original
population colonize a new population.
• The founders may not accurately represent the
genetic makeup of the original population
• Genetic diversity may decrease
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III. Genetic Drift
2. Founder Effect
Founder effect: a few members of an original
population start a new separate colony.
• The founders may not accurately represent the
genetic makeup of the original population
• Genetic diversity may decrease
Examples: Huntington’s disease among Afrikaners,
polydactyly among Amish
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IV. Natural Selection
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Is bigger always better?
Can being “average” be optimal?
When is it advantageous to be extreme?
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IV. Natural Selection
Types of Selection
1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
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IV. Natural Selection
1. Stabilizing Selection
Example: birth weight, # eggs
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IV. Natural Selection
2. Directional Selection
Examples: peppered moth,
antibiotic resistant bacteria
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IV. Natural Selection
3. Disruptive Selection
Example: beak size
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Exit Ticket – hand in before you leave!
1. Name one concept of evolution that you may have
heard about before today, but understand better now
after class. Explain that concept in your own words.
2. Name one concept or real-world example of a
concept that was completely new:
3. Write down a question about something that you do
not completely understand or are curious about.
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