1. Disruption of Genetic Equilibrium
Chapter 16 Section 2

2. Introduction
Evolution is the change in a population’s genetic material over generations
Change in a population’s allele frequencies
Any exception to the Hardy- Weinberg equilibrium can result in evolution

3. Mutation
Remember  the first condition for genetic equilibrium is no net mutations
Mutations can affect genetic equilibrium by producing new alleles for a trait
Most are harmful or have no effect
The few beneficial mutations will be passed on and eventually build up in a population

4. Gene Flow
Remember  The second requirement for genetic equilibrium is that the population size remains constant
Gene Flow - If individuals move their genes move with them
Immigration – Movement of individuals into a population
Emigration – Movement of individuals out of a population

5. Genetic drift
Remember  the third requirement of genetic equilibrium is the presence of a large population
Genetic drift - the alteration of the gene pool of a small population due to chance.
Northern Elephant seal – individuals are homozygous for all traits tested
Lost their genetic variation
Very susceptible to extinction

6. Two factors may cause genetic drift:
                                    
Bottleneck effect may lead to reduced genetic variability following some large disturbance that removes a large portion of the population. The surviving population often does not represent the allele frequency in the original population.
Founder effect may lead to reduced variability when a few individuals from a large population colonize an isolated habitat.

9. Nonrandom Mating
Remember  the fourth requirement of genetic equilibrium is random mating
Most species do not mate randomly, often influenced by geographic proximity
Sexual Selection – females chose the males they mate with based on certain traits

10. Extreme traits give the females an indication of the males fitness in his environment

11. Natural Selection
Remember  the fifth requirement of genetic equilibrium is the absence of natural selection
Natural selection means that some members of a population are more likely to survive and reproduce then others and contribute their genes to the next generation
Scientists observe 3 patterns of natural selection

12. Disruptive Selection
Individuals with either extreme of a trait have greater fitness then individuals with the average form of trait
Ex. Limpet
White shelled - found on rocks covered with white goose barnacles
Dark shelled - found on bare rocks
Intermediate individuals are easier to spot and get eaten by birds

13. Directional Selection
Individuals with one extreme of a trait have greater fitness then other individuals
Ex. Anteater – feeds by breaking open termite nests then pushes sticky tongue into nest to lap up termites
Anteaters with a long tongue would be able to eat more termites, this extreme would be favored over all other sizes

14. Stabilizing Selection
Individuals with average form of a trait have the highest fitness
Extreme for of traits have lower fitness
Ex.
A very large individual may be easier to spot by predators.
A small individual may not be able to run as fast