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. The Making of the Fittest Series HHMI
Video Explanation
The Making of the Fittest Series HHMI
“Natural Selection in Humans”

3. Individuals in Populations with Beneficial Genetic Traits Can Leave More Offspring
STEPS to EVOLUTION
Development of genetic variations
Occurs through mutations in reproductive cells
Natural selection
Acts on individuals
Genetically based traits enhance your ability to survive & reproduce
For natural selection to occur, a trait must be heritable & lead to differential reproduction

4. Summary of Biological Evolution
Genes mutate
Individuals are selected
Populations evolve
Are now better adapted to survive & reproduce under existing environmental conditions

5. Evolution by Natural Selection

6. 3 Choices! When environmental conditions change, populations Adapt
Migrate
Become extinct 6

7. 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

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

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

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

13. This is an example of disruptive selection because one phenotype is favored on the lava flows and the other is favored on the sandstone rocks.

14. The Making of the Fittest Series HHMI
Video Explanation
The Making of the Fittest Series HHMI
“Natural Selection and Adaptation”

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

16. Loss of Genetic Variation
The original population is on the left with three possible founder populations on the right.

17. 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

19. Founder Effect and Ellis-van Creveld Syndrome
Ellis–van Creveld syndrome often is the result of founder effects in isolated human populations, such as the Amish and some small island inhabitants. Although relatively rare, this disorder does occur with higher incidence within founder-effect populations due to lack of genetic variability. Observation of the inheritance pattern has illustrated that the disease is autosomal recessive, meaning that both parents have to carry the gene in order for an individual to be affected by the disorder.[3]

20. Other Mechanisms of Evolution
Sexual Selection occurs when traits increase mating success
Intrasexual selection is between males of same species

21. Intersexual selection occurs when males display traits that attract the female