Patterns of EvolutionEssential 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?

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A. Mechanisms of ChangeI. Genetic Variation

1. Mutations2. Sex Gene shuffling

II. Gene Flow (Migration)III. Genetic Drift

1. Bottleneck Effect2. Founder Effect

IV. Natural Selection1. Stabilizing Selection2. Directional Selection3. Stabilizing Selection

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How might variation occur in a single

population?

I. Genetic Variation

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I. Genetic Variation

1. Mutations

2. Sex Gene shuffling

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I. Genetic Variation1. 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 Variation1. 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 Variation1. 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 Variation2. Sex (gene shuffling)

How did this young wildebeest get so much variation in her DNA?

9A 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 DriftGenetic 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 DriftGenetic 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 decreaseExamples: 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 Selection1. Stabilizing Selection2. Directional Selection3. Disruptive Selection

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IV. Natural Selection1. Stabilizing Selection

Example: birth weight, # eggs

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IV. Natural Selection2. Directional Selection

Examples: peppered moth,antibiotic resistant bacteria

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IV. Natural Selection3. 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.