1. Evolution as Genetic Change
16:2

2. 1. Natural Selection
A. Natural selection will never act directly on genes. It acts on an entire organisms, not a single gene.
1. It only affects the individuals that survive and reproduce. If an organism dies, it does not contribute to the gene pool, if it survives and reproduces it does contribute.

3. 2. Natural selection on single-gene traits.
A. This can lead to changes in allele frequencies and evolution. Allele frequency is the number of times an allele occurs in a gene pool 16:1, and thus to evolution.

4. 3. Natural Selection on Polygenic Traits.
A. Polygenic is when a trait is controlled by more then one gene, and produce a range of phenotypes that often fit a bell curve. Fitness can vary a great deal from one end of a curve to the other. When fitness varies natural selection can act.
1. Directional – when an individual at one end of the curve have higher fitness than individuals in the middle or at the other end. The organism that displays a more extreme form of a trait, will have greater fitness than the average individual.
a. The range of phenotypes shift as some individuals fail to survive and reproduce while others succeed.

6. 2. Stabilizing Selection – when individuals near the center or the average form of the curve will have higher fitness than individuals at either end of the curve.

8. 3. Disruptive Selection –also called diversifying selection When individuals are at the upper or lower ends or, either extreme variation of the curve, have a higher fitness. This type of a selection could cause speciation. (creating a new species)

9. DISRUPTIVE SELECTION

10. 4. Genetic Drift
A .Random change in allele frequency in small populations. An allele can become more or less common, simply by chance, rather than if it has a negative or positive effect on fitness.
The smaller the population, the greater it has to experience this kind of change.

12. The Process of Speciation 16 :3

13. The Process of Speciation
A. Speciation - Formation of a new species.
1. Species is a group of organisms that breed with one another and produce fertile offspring. This means they would share a common gene
2. A genetic change in one individual can spread throughout the population as that individual and its’ offspring reproduce.
3. If this genetic change increases the fitness of the organism, that allele will eventually be found in many individuals of that population, forming a new species.

14. Isolating Mechanisms
A. As new species evolve, population become reproductively isolated from each other.
1. Reproductive isolation - When the members of 2 populations cannot interbreed and produce fertile offspring, they will have separate gene pools.

15. 2. 3 Different types of Reproductive isolation: a
2. 3 Different types of Reproductive isolation: a. Behavioral Isolation – 2 populations will not interbreed because of different courtship rituals or other strategies that involve behavior. Example – two types of meadow larks will not interbreed because they have different mating songs.

16. a. Geographic Isolation – 2 populations are separated by geographic barriers such as rivers, mountains or a body of water.
1. A river may be formed that could split a population in 2, stopping them from interbreeding causing speciation.
b. Temporal Isolation – 2 or more species reproduce at different times, such as orchids releasing pollen on different days, since they all only release it on a single day.