Lecture 11: Potential Exam Questions

What are the three essential requirements for natural selection?

1) There must be some variation for some trait. 2) Variation must be heritable. 3) There must be a greater or lesser probability of survival and reproduction due to possession of that trait.

What are the three types of natural selection and briefly describe them?

One type is stabilizing selection in which the population stabilizes on a specific trait and genetic diversity decreases. Another type is directional selection in which a single phenotype is favored and thus the population shifts in one direction. The third type is disruptive selection in which individuals at both extremes are favored so the population creates two separate peaks.

Explain tradeoffs and why they’re important.

Tradeoffs occur because an organism cannot put all of their resources into more than one character trait; ie. All resources into growth and reproduction all at once. Therefore, they have to choose one or the other. An example used in class was the Douglas Fir, which can either have many cones per tree and narrow ring width or wide ring width and few cones per tree. Another example used in class was the guppies in Trinidad. A fish can either be small and colorful or larger and not colorful.
