1. Daily Warm-up February 7th
What is genetic drift? What are the two types?
HW:
-Darwin video due tomorrow
-Read 21.4
Turn in:
-Nothing

2. 5 Evolutionary Agents Natural selection Sexual selection Mutation
Gene flow
Small population size (genetic drift)

3. Genetic Drift Chance events that take out alleles at random Two Types
Ex. Earthquake, flood
More pronounced in small populations
Two Types
Founder effect
Individuals become “founders” o f new population
Bottleneck effect
Population has experienced a “bottleneck” and certain alleles may be over-represented

4. Founder effect example

5. Cheetahs as a bottleneck example

6. Genetic Drift Significant in small populations
Causes allele frequencies to change at random
Can lead to a loss of genetic diversity
Can cause harmful alleles to be more prominent

7. Gene Flow
Transfer of alleles into or out of a population

8. In what sense is natural selection more predictive than genetic drift?
Question
In what sense is natural selection more predictive than genetic drift?

9. Natural Selection
Only agent that consistently causes adaptive evolution
Survival and reproductive advantage
Can be measure by relative fitness
Contribution to the gene pool by an individual relative to the other members of the population

10. 3 Types of Evolution
1. Directional selection= conditions favor individuals at one extreme

11. 2. Stabilizing Selection
Intermediate phenotype versions are selected for by conditions

12. 3. Disruptive Selection
Intermediate phenotype is selected against, both extremes selected for by conditions.

13. Sexual Selection
Traits that may or may not improve the likelihood of obtaining a mate
Sexual dimorphism- difference in
secondary sex characteristics
ex. Color, ornamentation, behavior
Intrasexual
Intersexual (mate choice)
*Birds of Paradise

14. Preservation of Genetic Variation
Neutral variation- genes that do not confer any advantage or disadvantage help maintain genetic variation
Also-
Diploidy- recessive allele is “hidden”
Balancing selection- natural selection keeps two or more forms in the population
Heterozygote advantage
Frequency-dependent

15. Heterozygote Advantage
When heterozygotes have greater fitness than either homozygous forms
Ex. Sickle-cell disease and
malaria

16. Frequency-Dependent Selection
Fitness of phenotype depends on how common in the population.
Ex. Fish in lake
Fungi in population of insects (see video)

17. Why doesn’t natural selection= perfect organism?
Selection can only act on existing variation
Evolution is limited by historical constraints
-Limited to ancestral structures
Adaptations are often compromises
Chance, natural selection, and environment interact