1. Biology
Chapter 11 Notes

2. Genetic variation
Gene pool- the combined alleles of all the individuals in a population
Allele frequency- a measure of how common a certain allele is in the population

3. Normal distribution
Phenotypes near the middle of the range tend to be more common, while the extremes are less common.

4. Directional selection
A type of selection that favors phenotypes at one extreme of a trait’s range.
Ex: low drug resistant bacteria to high drug resistant bacteria

5. Stabilizing selection
The intermediate phenotype is favored and becomes more common in the population.
Ex: wasps feed on small gall flies and woodpeckers feed on large gall flies

6. Disruptive selection
When both extreme phenotypes are favored by selection
Ex: blue- blue brown- dull brown lazuli buntings
Blue is dominant and see the other blue & blue brown as threats, leave the dull brown alone

7. Mechanisms of evolution
Gene flow- the movement of alleles from one population to another
Genetic drift- changes in allele frequency that are due to chance

8. Bottleneck effect
Genetic drift that occurs after an event greatly reduces the size of a population
Ex: over hunting

9. Founder effect
Genetic drift that occurs after a small number of individuals colonize a new area.
Ex: dwarfism in old order Amish communities

10. Speciation through Isolation
Reproductive isolation occurs when members of different populations can no longer mate successfully with one another.
Speciation is the rise of two or more species from one existing species

11. Behavioral isolation
Courtship dances, chemical scents, and courtship songs are signals for mating between populations
Behavioral isolation is caused by differences in these behaviors

12. Other isolations

13. Convergent evolution
Different species often must adapt to similar environments. Evolution toward similar characteristics in unrelated species is called convergent evolution.

14. Divergent evolution
When closely related species evolve in different directions.

15. Punctuated equilibrium
Episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary changes