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AP Biology, Chapter 25 Tracing Phylogeny Summary Introduction 1. Distinguish between phylogeny and systematics. a. Phylogeny is the evolutionary history of a group b. Systematics is the study of biological diversity in an evolutionary context THE FOSSIL RECORD AND GEOLOGICAL TIME Introduction Sedimentary rocks are the richest sources of fossils 2. Describe the process of sedimentation and the formation of fossils. Explain what portions of organisms mostly fossilize and why. a. Process i. Minerals and organisms settle in water ii. Organic substances decay iii. Minerals seep in and crystallize b. Hard parts fossilize most: decay/dissolve more slowly, or not at all Paleontologists use a variety of methods to date fossils 3. Distinguish between relative dating and absolute dating. a. Relative dating i. By position in the rockpile ii. Superposition: deeper, older; shallower, younger b. Absolute dating: in years based on isotopic analysis and half lives 4. Explain how isotopes can be used in absolute dating. a. Assumes we know the starting ratio of isotopes b. Assumes changes in the sample are due to radioactive decay alone c. Current ratio is measured; half-life used to calculate time d. Examples: C-14, K-40, U-238 e. Non-isotopic methods: racemization of L-amino acids The fossil record is a substantial, albeit incomplete, chronicle of evolutionary history 5. Explain why the fossil record is incomplete. a. Fossilization is rare i. Organism had to be buried ii. Remains had to remain undisturbed iii. Small chance of exposure by erosion iv. Small chance of being found b. Slanted toward fossils of long-lived, abundant, widespread species Phylogeny has a biogeographical basis in continental drift 6. Describe two dramatic chapters in the history of continental drift. Explain how those movements affected biological evolution. a. 250 million years ago; formation of Pangaea i. Once isolated populations became mixed ii. Habitat changes: less coastline, drier interiors b. 180 million years ago: break up of Pangaea i. Reinstated widespread geographical isolation ii. Current biogeographical patterns are the result The history of life is punctuated by mass extinctions followed by adaptive radiation of the survivors 7. Explain how mass extinctions have occurred and how they affected the evolution of surviving forms. a. Cambrian (?): evolution of hard body parts, increased predation b. Permian, 250 million years ago due to some combination of: i. Environmental changes related to the formation of Pangaea ii. Massive volcanic eruptions iii. Possible impact iv. Anoxic oceans 8. Describe the evidence related to the impact hypothesis associated with the Cretaceous extinctions. Describe the hypothesized consequences of such an impact. a. Evidence i. Iridium-rich layer on top of the Cretaceous rocks ii. Chicxulub; large crater of the right age b. Consequences i. Dust released blocked sunlight for years; photosynthesis blocked ii. Minerals released caused acid precipitation iii. Molten debris rained on North America PHYLOGENY AND SYSTEMATICS Introduction Taxonomy employs a hierarchical system of classification 9. Distinguish between systematics and taxonomy. a. Systematics is the study of biological diversity in an evolutionary context b. Taxonomy involves the identification and classification of species 10. Explain how species are named and categorized into a hierarchy of groups. a. Binomial i. Capitalized genus, non-capitalized species name ii. Underlined or in italics b. Hierarchy groups organisms into larger, more inclusive categories 11. List the major taxonomic categories from the most to least inclusive. a. Domain, kingdom, phylum, class, order, family, genus, species The branching pattern of a phylogenetic tree represents the taxonomic hierarchy Determining monophyletic taxa is key to classifying organisms according to their evolutionary history 12. Distinguish between homologous and analogous structures. Explain why the similarity of complex systems implies a more recent common ancestor. a. Homologous structures are inherited from a common ancestor b. Analogous structures i. Due to independent adaptation to similar selective pressure ii. = convergent evolution Molecular biology provides powerful tools for systematics 13. Explain how nucleotide sequences and amino acid sequences can be used to help classify organisms. Explain the advantages that molecular methods have over other forms of classification. a. Count the similarities: the more similar, the more closely related b. Advantages i. More objective and quantitative than comparing shapes ii. Can reveal relationships between seemingly identical or seemingly unrelated organisms c. Examples i. Protein comparisons of common proteins like cytochrome c ii. Hybridization, restriction maps and sequencing of DNA 14. Explain how molecular clocks are used to determine the approximate time of key evolutionary events. Explain how molecular clocks are calibrated in actual time. a. Basis of use i. Evolution of some proteins and DNAs is relatively constant ii. Number of substitutions is proportional to the time since divergence b. Calibrated by graphing the number of differences vs. known branch points 15. Explain how scientists determined the approximate time when HIV first infected humans. a. HIV evolves rapidly b. Samples of known age were sequenced c. Number of differences in sequence has been increasing d. Projection back to zero differences suggests in 1930 strain M entered humans The search for fossilized DNA continues despite recent setbacks: science as a process THE SCIENCE OF PHYLOGENETIC SYSTEMATICS Introduction Phenetics increased the objectivity of systematic analysis Cladistic analysis uses novel homologies to define branch points on phylogenetic trees 16. Define the parts and describe the interrelationships within a cladogram. Explain how a cladogram is constructed. a. Parts and interrelationships i. Evolutionary branches, or clades, are monophyletic .Mono-: all descendents having a certain trait; Amniota .Poly-: common trait but not from a common ancestor; endotherms .Para-: common trait, common ancestor, but not all descendents; reptiles ii. Branch points, or nodes, represent common ancestors iii. Sequence of branching represents historical chronology b. Construction i. Make a character table characters vs. taxa ii. The more common the character, the farther down the branch point 17. Distinguish between shared primitive characters and shared derived characters. Compare the definitions of an ingroup and outgroup. a. In placing two taxa on a cladogram i. Shared derived characters were unique to their common ancestor ii. Shared primitive characters predates that ancestor b. Groups i. Outgroup: species somewhat related to the group under study ii. Ingroup: the more closely related group under analysis 18. Compare the cladistic and phylocode classification systems. a. Cladistic classification retains and creates taxon names b. Phylocode includes only the clades with imposing hierarchical levels 19. Explain the principle of parsimony. Explain why any phylogenetic diagram is viewed as a hypothesis. a. Parsimony favors the simplest explanation consistent with the facts b. Phylogenetic trees are hypotheses i. Characters may later be shown to be analogous ii. More characters might suggest a different branch pattern Phylogenetic systematics relies on both morphology and molecules 20. Describe an example of a conflict between molecular data and other evidence, such as the fossil record. Explain how these differences can be addressed. a. Origin of major mammalian orders i. Molecular clocks indicate divergence 100 mya ii. Fossil evidence gives 60 mya b. Orders might have originated 100 mya but became common 60 mya