1. Gene Pool- all the genes in a population

2. Prerequisites Process Outcome Trait is heritable Variation for trait
Traits causes differences in survival and reproduction
Individuals with favorable traits are more likely to survive/
reproduce & pass down these favorable genes.
A change in the gene pool with the favorable genes becoming more common.
Adaptation for the environment.

3. Normal Distribution
A normal distribution is one that forms a bell-shaped curve. (variation in trait on the X axis, number of individuals on the Y axis)
Example: Height in females: Average height is 5’4’’

4. Types of Natural Selection
Directional selection:
Favors individuals with traits that are at one end of a distribution.
Results in the distribution shifting, with an increase in the favorable form.

5. Types of Natural Selection
Stabilizing selection:
Eliminates individuals at both ends of the spectrum.
Results in a narrower distribution ; the average remains the same.

6. Types of Natural Selection
Disruptive selection:
Eliminates average individuals, but favors individuals at either extreme of the spectrum of variation.
Results in a bimodal distribution, with fewer of the average form and more of the extremes.
© Brooks/Cole Publishing Company / ITP

7. On an island, prickly pear cacti with the lowest branches are more likely to be eaten by iguanas. Which kind of selection is this and how could the distribution change? Directional selection; could result in taller prickly pear trunks (higher branches).

8. Chimpanzee babies are more likely to survive birth if they are not too large or too small. Which kind of selection is this and how could this change the distribution? Stabilizing selection; could result in a narrower distribution of birth size.

9. On an island, dragonflies with longer wings are more likely to get blown out to sea. Which type of selection is this, and how could it change the distribution of wing length. Directional selection; could result in the average wing length decreasing.

10. A species of begonia on average flowers in August
A species of begonia on average flowers in August. Its pollinators become less active in August due to the heat. Which type of selection is this, and how could the distribution change? Disruptive selection; could result in fewer plants that flower in midsummer, more in the early and late summer.