1. Warm Up Describe natural selection and how this leads to evolution.

2. What is a mechanism?

3. Mechanisms of Evolution
Natural Selection
Population Genetics
Genetic Drift
Gene Flow
Nonrandom mating
Mutation

4. Individuals in a population show variations.
Evolution
Natural Selection
Population Genetics
Individuals in a population show variations.
Variations can be inherited.
Organisms have more offspring than can survive on available resources.
Variations that increase reproductive success will have a greater chance of being passed on.

5. Acts on an organisms phenotype and change allele frequencies.
Natural Selection
Acts to select the individuals that are best adapted for survival and reproduction.
Acts on an organisms phenotype and change allele frequencies.

6. Allele Frequencies

7. Types of Natural Selection
Stabilizing Selection
Directional Selection
Disruptive Selection
Sexual Selection

8. Types of Natural Selection
Evolution
Types of Natural Selection
Stabilizing selection
average phenotype has the highest fitness
eliminates extreme phenotypes

9. Types of Natural Selection
Evolution
Types of Natural Selection
Directional selection
One Extreme phenotype has the highest fitness
Selection in one direction makes an organism more fit.

10. Types of Natural Selection
Evolution
Types of Natural Selection
Disruptive selection
Splits population into two groups.
Extreme phenotypes have higher fitness than the average phenotype

11. Types of Natural Selection
Evolution
Types of Natural Selection
Sexual selection
In populations where males and females differ significantly in appearance.

12. Sexual Selection
Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival.

13. Stabilizing Selection
Evolution
Natural Selection
Stabilizing Selection
Directional Selection
Disruptive Selection

14. Greater in smaller populations Greater Chance of losing an allele
Evolution
Genetic Drift
A change in the allele frequencies in a population that is due to chance
Greater in smaller populations
Greater Chance of losing an allele

15. Small Population (Genetic Drift)
Evolution
Genetic Drift
Small Population (Genetic Drift)

16. Genetic Drift
Founder Effect
Bottleneck

17. Genetic Drift Founder Effect
Evolution
Genetic Drift
Founder Effect
small part of a population settles in a location separated from the rest of the population
Alleles that were uncommon in the original population might be common in the new population.

18. population declines to a very low number then rebounds
Genetic Drift
Evolution
Bottleneck
Occurs when:
population declines to a very low number
then rebounds

19. Genetic Drift Bottleneck Population Decreases The Survivors Repopulate
Evolution
Bottleneck
Population Decreases
The Survivors Repopulate
What is Different?
Why could less diversity be bad?
Less Diversity

20. Increases genetic variation within a population
Evolution
Gene Flow
Increases genetic variation within a population
reduces differences between populations

21. Nonrandom Mating Promotes inbreeding
Evolution
Nonrandom Mating
Promotes inbreeding
could lead to a change in allele proportions favoring individuals that are homozygous for particular traits

22. Chapter 15
Evolution
15.3 Shaping Evolutionary Theory
Gene Flow
Increases genetic variation within a population and reduces differences between populations
Nonrandom Mating
Promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits

23. Mutation Random change in genetic information
Cause changes in allele frequencies
Some advantageous

24. Speciation Species diverge Can occur due to isolation
Become two separate species that cannot reproduce
Allopatric speciation
Sympatric speciation

25. Isolation Reproductive Isolation
gene Flow is prevented between two populations of the same species.
different mating seasons

26. Isolation Geographic Isolation
A population that becomes divided (isolated) by a physical barrier
Each groups evolves differently

27. Chapter 15
Evolution
Abert squirrel
Kaibab squirrel

28. Allopatric Speciation Sympatric Speciation
Evolution
Allopatric Speciation
Sympatric Speciation
A species evolves into a new species without a physical barrier.
A physical barrier divides one population into two or more populations.

29. Which is not a principle of Darwin’s theory about
Chapter 15
Evolution
Chapter Diagnostic Questions
Which is not a principle of Darwin’s theory about
the origin of species?
Individuals show variations.
Variations can be inherited.
Organisms have more offspring than
available resources will support.
Offspring always inherit the best traits.

30. Which description is evidence that a speciation has taken place?
Chapter 15
Evolution
15.3 Formative Questions
Which description is evidence that a
speciation has taken place?

31. A physical barrier has caused two groups from a
Chapter 15
Evolution
15.3 Formative Questions
A physical barrier has caused two groups from a
population to adapt to different environments.
Some members can no longer produce fertile
offspring with members of the original population.
A small group has developed mating behaviors that
are different than those of the rest of the population.
Some members from a population have developed
physical characteristics that are different than the
original population.

32. Within a population of squirrels, those that
Chapter 15
Evolution
Standardized Test Practice
Within a population of squirrels, those that
live higher in the mountains where it is
cooler have long fur. Squirrels that live in
the foothills where it is warmer have short
fur. The original population is believed to
have had intermediate fur length. Which
graph represents this type of natural
selection?

33. Standardized Test Practice
Chapter 15
Evolution
Standardized Test Practice

34. Contrast the four types of natural selection.