How is genetic variation preserved and potentially even promoted in a population?

I. Diploidy - For every gene there are (at least) two copies because almost every species on the earth currently is sexually reproducing. What does this do for us?
     A. Allows recessives to exist. (Example: white skin. Dark skin is very common among people along the equator. This prevents skin cancer from the sun but when our ancestors moved out of Africa, we developed light skin because we didn't have to worry about skin cancer as much and light skin allows us to absorb the sun and make our own Vitamin D.)
     B. Allows codominance. (Example: African people want to be heterozygous for Sickle Cell Anemia because the recessive protects against Malaria. This could not happen without Diploidy.)

II. Meiosis
     A. Crossing Over - It is the number 1 factor for genetic variation in gametes.
     B. Independent Assortment - the number 2 factor for genetic variation - two chromosomes separating do not affect each other (flipping two coins). This exponentially magnifies the variation from crossing over.

III. Sexual Reproduction
     A. Two parents' genetic info is randomly passed to offspring. (You are not the same as your siblings.)
     B. Mechanisms that promote outbreeding. (the opposite of inbreeding - we think marrying our cousins is gross and flowering plants promote outbreeding because they attract pollenators.)

IV. Clines - Happens when a population's genetics change from one side of its range to another.

V. Ecotype - genetic variation types of the same species because they live in different ecosystems.