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Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in Holtzclaw

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Page 1: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Mechanisms of Evolution

Concept 4: Analyzing the evolution of populations through

Hardy-Weinberg (microevolution)Chapter 23 in Campbell, pg 155-158 in Holtzclaw

Page 2: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Goal: To analyze how populations change over time

Page 3: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

The Evolution of Populations

You must know: How mutation and sexual reproduction each

produce genetic variation The conditions for Hardy-Weinberg

Equilibrium How to use the Hardy-Weinberg equation to

calculate allelic frequencies, to test whether a population is evolving.

Page 4: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Genetic Variation

Crossing Over Independent

Assortment Fertilization

Gene pool = a population’s genetic make-up

Page 5: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Remember...

Homozygous...(dominant)(recessive)

Heterozygous...(dominant will “show”)

Page 6: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Preservation of Genetic Variation

Diploidy – “hiding” recessive alleles

Heterozygote advantage Ex) sickle cell anemia - malaria

Page 7: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

What alters allele frequencies?

Three major factors:1. Natural Selection – causes adaptive evolution

2. Genetic Drift Founder Effect Bottleneck Effect

3. Gene Flow

(Mutations also alter allele frequencies, but rare)

Page 8: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Natural Selection – causes adaptive evolution

Relative Fitness Fitness compared to other members of the

population… (your contribution to the gene pool of the next generation!)

Three ways natural selection can work: Directional selection Disruptive selection Stabilizing selection

Page 9: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in
Page 10: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in
Page 11: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in
Page 12: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in
Page 13: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Try This!

In what sense is natural selection more “predictable” than genetic drift?

Page 14: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Try This!

In what sense is natural selection more “predictable” than genetic drift? Natural Selection:

Alters allele frequency in a nonrandom way Tends to increase the frequency of alleles that

increase an organism’s fitness and decrease the frequency of alleles that decrease an organism’s fitness

Genetic Drift: Alters allele frequency by chance alone

Page 15: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Introducing…The Hardy-Weinberg Principle!

Clarifies the factors that alter allele frequency

A non-evolving population is in Hardy-Weinberg equilibrium.

Page 16: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Conditions for Hardy-Weinberg Equilibrium:

No mutations Random mating No natural selection Extremely large population size

(no genetic drift) No gene flow

Page 17: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

The Hardy-Weinberg Formula

p2 + 2pq + q2 = 1

where p + q = 1See Handout...

Page 18: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Try This!

In a certain population of 1000 fruit flies, 910 have red eyes while the remainder have sepia eyes.

The sepia eye trait is recessive to red eyes. How many individuals would you expect to be

homozygous for red eye color?

Hint: The first step is always to calculate q2! Start by determining the number of fruit flies that are homozygous recessive…

Page 19: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Try This! Answer:

You should expect 490 to be homozygous dominant.

Calculations:q2 for this population is 90/1000 = 0.09q = = 0.3p = 1 - q = 1 - 0.3 = 0.7The homozygous dominant frequency = p2 = (0.7)(0.7) = 0.49.Therefore, you can expect 49% of 1000, or 490 individuals, to be homozygous dominant.

Page 20: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

Now… Handout!

Page 21: Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg 155-158 in

The Evolution of Populations

Do you know? How mutation and sexual reproduction each

produce genetic variation The conditions for Hardy-Weinberg

Equilibrium How to use the Hardy-Weinberg equation to

calculate allelic frequencies, to test whether a population is evolving.