AP Biology Exam Review 2002-2003

1. AP Biology Exam Review2002-2003 Heredity and Evolution – 25%

2. Evolutionary biology – 8% • Early evolution of life • Evidence of evolution • Mechanisms of evolution

3. Related fields of study • Paleontology: study of fossils • Comparative anatomy: study of structural similarities among organisms • Comparative embryology: study of embryological similarities among organisms • Taxonomy: study of organism groupings with similar homologous structures (including vestigial organs) • Biochemistry: chemical reactions in living things

4. Terminology • Population: localized group of individuals of the same species • Species: group of population whose individuals have the potential to interbreed and produce fertile offspring • Gene pool: total aggregate of all genes in a population at any given time

5. Tenets of evolution • Natural selection “edits” the available gene pool for a species. • Natural selection is contingent upon time and place. Certain variations in a population (group of species residing in one area) are more favored for survival than others. • Mutations are a sources of variation in a population. • “Descent with modification”

6. DDT & Insects • Insects with DDT resistance also have reduced metabolism. • Without DDT present, these insects are not adapted for the environment.

7. Homology vs. Analogy

8. Three kinds of homologies – having common origin • 1. Anatomical homology: example, forelimbs • 2. Embryological homology: example, Eustachian tube in humans and all mammals • 3. Molecular homology: DNA, RNA as genetic code (shown through RFLP analysis)

9. Molecular homology • Human hemoglobin has 146 amino acids total.

10. Sugar glider vs. Flying squirrel Convergent evolution

11. Genetic drift Changes to allele frequencies in population due to random chance

12. Bottleneck effect • Genetic drift due to drastic reduction in allele frequencies What factors can cause bottleneck effect?

13. The founder effect • Members from a larger population colonize an isolated region. (Ex: primary, secondary succession) • Ex: 15 people founded a British colony in 1814, midway in the Atlantic Ocean. One colonist had retinitis pigmentosa, a recessive degenerative blindness. Today, there is a higher frequency of this disorder than most places on Earth.

14. Gene flow • Genetic exchange due to migration of fertile individuals or gametes between populations • Ex: wind carrying pollen grains with sperm from plant to far off locations

15. Mutations • Changes to an organism’s DNA • Changes in the DNA, if occurring in gametes, can be passed down to the next generation. • Quantitative changes to the population can only result if organisms with the mutation produce a disproportionate number of offspring.

16. Variations in the population • Polymorphism: For any characteristic, there are more than two “morphs” (forms). • A variation of the characteristic can only be considered one of the morphs if there is a high enough frequency in the population.

17. Measuring diversity • Gene diversity: measuring whole gene differences • Nucleotide diversity: measuring differences at the molecular level (using RFLP analysis or genomic comparisons)

18. Geographic diversity • Differences in gene pools between populations or within subgroups of populations • Cline: graded change in some trait along a geographic axis

19. Cline

20. What preserves variation • Mutation • Sexual recombination (meiosis) • Diploidy • Balanced polymorphism: ability to maintain stable allele frequency (established through heterozygote advantage and frequency-dependent selection) • Neutral variation

21. Directional selection

22. Limitations of natural selection • 1. Limited to historical constraints • 2. Adaptations are often compromises. • 3. Not all evolution is adaptive. • 4. Selection can only edit existing variations.

23. Hardy-Weinberg equation of non-evolution • No natural selection • No mutation • No migration • Large population • Random mating • p2 + 2pq + q2 = 1 • p + q = 1

24. Hardy-Weinberg equation • p = frequency of dominant allele in the population (A) • q = frequency of recessive allele in the population • p2 = AA (homozygous dominant genotype) • 2pq = Aa (heterozygous genotype) • q2 = aa (homozygous recessive genotype) • p2 + 2pq = dominant phenotype • q2 = recessive phenotype

25. Sample H-W problem • Hint to solving these equations: LOOK FOR THE PERFECT SQUARE!! SOLVE FOR Q! • In a population of 100 individuals, 91 in the population show the dominant phenotype. What is the frequency of the dominant allele in this population? • (100 – 91)/100 = recessive phenotype = q2 • .09 = q2 q = .3 p+q = 1 p = .7

26. The Origin of Species In what circumstances would new species evolve from preexisting species?

27. Reproductive barriers helps to preserve species. • Any factors that impedes the reproduction of members within a species • Without the ability to breed together, the gene pool is isolated. (no migration)

28. Two types of barriers • Prezygotic barriers: prevents fertilization of ova (egg) • Postzygotic barriers: following fertilization, hybrid zygote unable to develop into viable offspring

29. Prezygotic barriers • Habitat isolation • Behavioral isolation • Temporal isolation • Mechanical isolation • Gametic isolation

30. Postzygotic barriers • Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown

31. Other definition of species • Ecological: niche (set of environmental resources an organism uses) • Pluralistic: more than one way to define species • Morphological: organisms with unique set of structural features • Geneological: organisms with unique genetic history

32. Interrupting gene flow • Changes to the gene pool can ultimately lead to evolution of new species. • This is called speciation.

33. Patterns of speciation • Anagenesis: phyletic evolution, accumulation of heritable change in a population • Cladogenesis: branching evolution, (basis for biological diversity)

34. *Three modes of speciation* • Allopatric speciation: geographic separation leads to new species if organisms evolve reproductive barriers • Sympatric speciation: small population within parent population becomes new species • Adaptive radiation: ancestral species colonize an area where diverse geographic or ecological conditions are available, rapid evolution

35. Allopatric vs. Sympatric • What factors can lead to each type of speciation?

36. Allopatric speciation • Geographic barriers (mountains, valleys, etc) can separate the ability for breeding between members of the same species. • Ring species: species that seemingly are in the gradual process of divergence from a common ancestor

37. Adaptive radiation • Much like allopatric speciation • Island chains have geographic isolation but are close enough for occasional have hybrids between populations.

38. How reproductive barriers evolve • Diane Dodd’s experiment showing allopatric speciation leading to reproductive barrier (therefore new species)

39. Allopatric speciation

40. Sympatric speciation in plants • Autopolyploid: organism with more than normal chromosome # due to meiotic failures. • 4N can breed with 4N  8N offspring (polyploid) • In one generation, postzygotic barriers form, causing reproductive isolation.

41. Allopolyploid • Members of two different species create a hybrid that cannot back breed with parents. The hybrid is more vigorous (*hybrid vigor*) enables hybrid to reproduce asexually  may eventually evolve sexual reproduction.

42. Sympatric speciation • Fishes in Lake Victoria (East Africa) demonstrate that females may select mates based on coloration. • Overtime, the nonrandom mating leads to behavioral isolation, and a new species of fish arise within the parental population.

43. Punctuated equilibrium • Sudden appearance of organisms in the phylogenetic tree

44. Micro vs. Macroevolution • Microevolution: changes in gene (allelic) frequency over generations; Hardy & Weinberg • Macroevolution: level of change in organisms that is evident in the fossil record (requires long period of time) • Speciation bridges microevolution and macroevolution.

45. Patterns of evolution • Divergent evolution: Two or more species originate from the same ancestral species. • Convergent evolution: Two unrelated species share many characteristics. • Parallel evolution: Two related species after divergence evolve similar characteristics. • Coevolution: symbiotic relationships

46. Origin of life • Oldest fossils = 3.5 billion years old, indicating maybe oldest life form 1 billion years old • Cyanobacteria: earliest fossilized organisms • Common metabolic pathway in all organisms: glycolysis • Primitive atmosphere: hydrogen, methane, ammonia, water vapor (reducing atmosphere)

47. Chemical evolution • 1. Earth and its atmosphere formed. • 2. Primordial seas formed. • 3. Complex molecules synthesized. • 4. Polymers and self-replicating molecules were synthesized. (proteinoids) • 5. Organic molecules were concentrated and isoaltred into protobionts. • 6. Primitive heterotrophic prokaryotes formed. • 7. Primitive autotrophic prokaryotes formed. • 8. Oxygen and ozone layer formed. • 9. Eukaryotes formed.

48. Endosymbiotic theory • Mitochondria and chloroplast have their own circular and “naked” DNA. • M & C ribosomes similar to bacteria. • M & C divide independently much like binary fission. • Thylakoid membranes of chloroplast resemble membranes of cyanobacteria.

49. Origin of life experiments • Oparin and Haldane: able to produce coacervates that could take in enzymes; predicted simple molecules form when oxygen absent • Stanley Miller: able to synthesize simple organic compounds with flash of electricity (“lightning”); tested Oparin and Haldane’s hypotheses • Melvin Calvin: complex molecules formed from polymerization • Sidney Fox: microspheres (protenoids)

50. Chemical selection • Aggregates with most stable compounds remained. • Chemical reactions that preserved aggregates enabled aggregates to remain. • Nonliving  living: able to store and use energy (metabolism), able to pass on genetic information