a. Evolution is change in the genetic composition of a population over time. If a population is not changing, i.e. if it has the same allele and genotype frequencies from generation to generation, the population is in equilibrium (no evolution is occuring).

b. Sexual reproduction alone does not change gene frequencies. In and of themselves, Mendel's Laws will not result in evolution (or changes in gene frequencies).

c. Assumptions of the Hardy-Weinberg Equilibrium:

i. individuals choose mating partners at random (random mating); reproduction is sexual not asexual

ii. there is no mutation

iii. there is no migration (no gene "flow" between populations)

iv. the population is large

v. there is no selection (all individuals survive and reproduce equally well)

d. What does Hardy-Weinberg say?

If all of the assumptions are met, then gene and genotype frequencies will not change from generation to generation. Evolution will not occur.

e. The particulars...

(frequency of allele A ) + (frequency of allele a ) = 1 p + q = 1

(frequency of genotype AA) + (freq. genotype Aa) + (freq. genotype aa) = 1

If the genotype frequencies in a population deviate significantly from predicted Hardy-Weinberg frequencies, that is evidence for the action of some evolutionary agent; something of evolutionary interest is influencing the population.

a. Evolutionary agent that changes genotype frequencies without changing allele frequencies

i. Nonrandom mating

b. Evolutionary agents that change allele frequencies without natural selection

i. Mutation

ii. Migration

iii. Small population ‡ genetic drift (chance alone can alter gene frequencies in small populations)

- bottleneck (cheetah)

- founder effect (africanized bees; Pitcairn Islanders)

c. Natural Selection! (topic of the next lecture...)