1. Population bottlenecks often result in reduced or no genetic variation.

2. Small populations experience genetic drift, founder events, and population bottlenecks. Each causes a loss in genetic variation. Allele becomes fixed = no variation. + genetic drift

3. ***Summarize the results. What is the potential consequence for small populations? Population size % polymorphic genes

4. Assortative mating: when individuals choose mates non-randomly with respect to their own genotypes. Negative: mates differ genetically --> increases proportion of heterozygotes Most individuals do this to avoid inbreeding. Positive: like mating with like (includes inbreeding) --> increases proportion of homozygotes

5. Positive assortment increases the proportion of homozygotes unmasks deleterious recessive alleles = inbreeding depression ***Does it directly change allele frequencies or only the frequencies of genotypes?

6. % homozygosity depends on level of inbreeding.

7. ***What are mechanisms to avoid inbreeding? dispersal recognition of close relatives negative assortative mating genetic self-incompatibility ***When can inbreeding be beneficial? Individual is capable of reproduction without pollinator or mate Organisms are adapted to local conditions---> best to retain genotype and not mix up.

8. Optimal outcrossing distance: ***Summarize the main results. Provide a possible explanation for them.

9. Gene flow (migration)--> mixes alleles between subpopulations and homogenizes them. Maintains genetic variation ***What represents gene flow in animals? plants? Animals: dispersal of the adult animal or gametes Plants: dispersal of pollen and seeds

10. Gene flow impeded by a physical barrier. Do separated populations have a different genetic structure? Will this lead to speciation?

11. Evolution by natural selection… Finches beak size changes in response to change in seed hardness in drought years.

12. Natural selection: change in the frequency of traits in a population because of differential survival and reproduction of individuals with those traits. Individuals with the most offspring are selected and the proportion of their genotypes increases over time. Fitness: the genetic contribution by an individual to future generations. Relative fitness: Maximum = 1 = most fit

13. Types of natural selection: Intermediates most fit Extremes most fit Two extremes favored at same time Most commonRemoves Uncommon in unchanging genetic Retains variation environments; variation Removes variation

14. ***Which type of selection acts on hatch date? What might be the selective agent?

15. Directional selection on beak depth

16. Disruptive selection increases phenotypic variation in a population. A dimorphism in beak size

17. Frequency-dependent selection: –genes are selected for when at low frequency and against when at high frequency –Maintains genetic variation

18. Summary of forces Remove genetic variation: Natural selection Small population size Maintain genetic variation: Mutation Gene flow Heterozygote superiority Frequency-dependent selection Varying selective pressures in time and space

19. Gene flow homogenizes differences between subpopulations. Natural selection differentiates subpopulations. Which is stronger: gene flow or natural selection? Is it different between plants and animals?

20. ***Sample exam question. A species of scale insects extracts fluids from branches of pine trees. They have very limited movement. In an experiment, these insects were transplanted 1) between branches of the same pine tree, and 2) from one pine tree to another pine tree of the same size.

21. 1.State the hypothesis/prediction that was being tested as an “If…then…” 2.Summarize the results in one concise sentence. 3.Do the results support the hypothesis? 4.Predict whether gene flow or natural selection would be a more powerful force affecting the genetic structure of this insect. Explain your choice. 5. Predict whether the genetic makeup of populations of the insect on adjacent trees would be homogeneous or differentiated. Explain your choice.

22. Objectives Define (micro)evolution and its relation to genetics Sources of genetic variation Forces causing change in gene frequency in pop Small population size Assortative mating Gene flow Natural selection Which force(s) maintain vs. eliminate genetic variation? Which force is strongest in plants? animals?

23. Vocabulary