1. Evolution of Populations
What are the three ways that natural selection can change the distribution of a trait?
How does genetic drift lead to the evolution of populations?

2. Natural Selection in Populations
Traits are normally distributed in a bell- shaped curve
Microevolution is the change in the frequencies of alleles over time
The frequencies can change in one of three ways

3. Natural Selection in Populations
Directional Selection occurs when one extreme phenotype is favored

4. Natural Selection in Populations
Stabilizing Selection occurs when intermediate phenotypes are favored

5. Natural Selection in Populations
Disruptive Selection occurs when both extreme phenotypes are favored

6. Other Mechanisms of Evolution
Gene flow – movement of alleles between populations
Increase in movement, increases genetic variation
Decrease in movement, decreases genetic variation but increases evolution of new species

7. Other Mechanisms of Evolution
Genetic drift
Changes in allele frequency due to chance
Affects small populations more than large populations
Two causes:
Bottleneck effect – event reduces size of population
Founder effect – small number of individuals colonize a new area

9. Founder Effect and Ellis-van Creveld Syndrome

10. Other Mechanisms of Evolution
Sexual Selection occurs when traits increase mating success
Intrasexual selection is between males of same species
Intersexual selection occurs when males display traits that attract the female