1. Population Genetics

2. The Gene Pool
Members of a species can interbreed & produce fertile offspring
Species have a shared gene pool
all of the alleles of all individuals in a population

3. The Gene Pool Different species do NOT exchange genes by interbreeding
Different species that interbreed often produce sterile or less viable offspring e.g. Mule

4. Populations A group of the same species living in an area
No two individuals are exactly alike (variations)
More Fit individuals survive & pass on their traits

5. The Hardy-Weinberg Principle
Used to describe a non-evolving population. 
 Natural populations are NOT expected to actually be in Hardy-Weinberg equilibrium.
Deviation from Hardy-Weinberg equilibrium usually results in evolution
Understanding a non-evolving population, helps us to understand how evolution occurs

6. 5 Assumptions of the H-W Principle
Large population size - small populations have fluctuations in allele frequencies (e.g., fire, storm).
No migration - immigrants can change the frequency of an allele by bringing in new alleles to a population.
No net mutations - if alleles change from one to another, this will change the frequency of those alleles

7. 5 Assumptions of the H-W Principle
Random mating - if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.
No natural selection - if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

8. Speciation Formation of new species
One species may split into 2 or more species
A species may evolve into a new species
Requires very long periods of time

9. Methods of speciation
Allopatric speciation: a physical barrier divides one population into two or more populations
Sympatric speciation: a species evolves into two ore more different species within the same environment

10. Patterns of evolution that lead to speciation
Adaptive radiation
Aka divergent evolution
When one species gives rise to many species in response to the creation of new habitat or ecological opportunities (new food source)
Often follows mass extinctions
Coevolution
When the evolution of one species affects the evolution of another species

11. Patterns of evolution that lead to speciation
Convergent evolution
When unrelated species evolve similar traits even though they live in different parts of the world
Similar ecology and climates in different geographical areas
Could lead to analogous structures

12. 5 Causes of evolution 1. Genetic Drift
the change in the gene pool of a small population due to chance
Two types:
Bottle neck effect
Founders effect

13. Factors that Cause Genetic Drift
Bottleneck Effect
a drastic reduction in population (volcanoes, earthquakes, landslides …)
Reduced genetic variation
Smaller population may not be able to adapt to new selection pressures

14. Loss of Genetic Variation
Cheetahs have little genetic variation in their gene pool
This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age

15. Founder Effect
occurs when a new colony is started by a few members of the original population
Reduced genetic variation
May lead to speciation

16. 2. Natural Selection - Cause ADAPTATION of Populations
- success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance)
- Cause ADAPTATION of Populations

17. 3 Modes of Natural Selection
Directional Selection
Favors individuals at one end of the phenotypic range
Most common during times of environmental change or when moving to new habitats
Disruptive selection
Favors extremes over intermediate phenotypes
Occurs when environmental change favors an extreme phenotype

18. 3 Modes of Natural Selection
Stabilizing Selection
Favors intermediate over extreme phenotypes
Reduces variation and maintains the curent average
Example: Human birth weight

20. 3. Gene Flow 4. Mutation 5. Non-random mating
-is genetic exchange due to the migration (immigration or emigration) of fertile individuals or gametes between populations
4. Mutation
a change in an organism’s DNA
Mutations can be transmitted in gametes to offspring
5. Non-random mating
Mates are chosen on the basis
of the best traits

21. Preventing speciation
Prezygotic isolation: mechanisms that prevent reproduction by making fertilization unlikely
Prevent new genotypes from entering a gene pool through geographic, ecological and behavioral differences
Temporal isolation: timing differences prevent interbreeding
Ex: closely related species of fireflies mate at different times of night
Behavioral isolation: mating behaviors prevent interbreeding
Ex: differences in mating calls between closely related species of birds

22. Preventing speciation
Postzygotic isolation: mechanisms that prevent a hybrid (offspring of interbreeding) from surviving or reproducing
When two different species reproduce, their offspring are typically infertile
Ex: ligers are the product of a male lion and female tiger mating and are sterile
Lions are tigers are different species but are close enough to interbreed

23. How fast does evolution occur?
Two theories:
Gradualism: evolution proceeds in small, gradual steps
Punctuated equilibrium: rapid spurts of genetic change cause species to diverge quickly
- small periods of change, large periods of no change

24. Allopatric speciation Sympatric speciation Adaptive evolution
On pg 110 draw illustrations for the following terms/phrases to help you remember them:
Hardy- Weinberg
Speciation
Allopatric speciation
Sympatric speciation
Adaptive evolution
Coevolution
Convergent evolution
Genetic drift
Founder’s effect
Bottleneck effect
Directional selection
Disruptive selection
Stabilizing selection
Gene flow
Prezygotic isolation
Postzygotic isolation