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Chapter 26 Phylogeny and the Tree of Life

Chapter 26 Phylogeny and the Tree of Life. Chapter focus. Shifting from the process of how evolution works to the pattern evolution produces over time. Phylogeny. Phylon = tribe, geny = genesis or origin

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Chapter 26 Phylogeny and the Tree of Life

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  1. Chapter 26Phylogeny and the Tree of Life

  2. Chapter focus • Shifting from the process of how evolution works to the pattern evolution produces over time.

  3. Phylogeny • Phylon = tribe, geny = genesis or origin • The evolutionary history of a species or a group of related species.

  4. Systematics • The study of biological diversity and classification. • Uses evidence from the fossil record and other sources to reconstruct phylogeny.

  5. Systematics fuses: 1. Phylogeny- tracing of evolutionary relationships. 2. Taxonomy- the identification and classification of species.

  6. Taxonomy • Natural to humans. • Modern system developed by Linnaeus in the 18th century.

  7. Scientific names • Composed of Genus and species. • Written in Latin and shown in italics or underlined. • Governed by a set of rules and procedures. • Are subject to changes.

  8. Linnaeus Taxonomy 1. Binomial Nomenclature – two names for each organism. Ex - Homo sapiens 2. Hierarchical System – arranges life into groups. Ex - Kingdom  Species

  9. Modern System

  10. Goal of Systematics • To have Taxonomy reflect the evolution or phylogeny of the organisms.

  11. Phylogenetic Tree • Branching diagram showing evolutionary relationships between organisms. • Recreation of Darwin’s Tree of Life.

  12. Phylogenetic tree – Ex.

  13. Trees show: • Ancestral lineage • Branch points or nodes • Length of branch point suggests “time” and degree of closeness.

  14. Phylogenetic tree – Ex. Ancestral Lineage Branch point

  15. Question? • How to group taxa so that the phylogenetic relationships are correct ? • Use evidence to date, but the relationships (and trees) will change as new data is obtained.

  16. Ideal Situation • Monophyletic Grouping - a single ancestor gave rise to all species in the taxon.

  17. Other Possibilities • Polyphyletic - grouping where members are derived from two or more ancestral forms. • Paraphyletic - grouping that does not include all members from an ancestral form.

  18. Problem • Not all “likeness” is inherited from a common ancestor. • Problem is of homology vs analogy.

  19. Homology and Analogy • Homology – likeness attributed to shared ancestry. • Ex: forelimbs of vertebrates • Analogy – likeness due to evolution solution for the same problem. • Ex: wings of insects and birds

  20. Convergent Evolution • When unrelated species have similar adaptations to a common environment. A specific example of Analogy. • Ex: Sharks and dolphins

  21. Only 1 is a “mole”

  22. Only one is a “cactus”

  23. Need • Methods to group organisms by similarities and phylogenies. • One possible method is Molecular Systematics.

  24. Molecular Systematics • Compares similarities at the molecular level. • Ex: DNA, Proteins

  25. DNA patterns • If similar DNA – more closely related, more recent common ancestor. • If different DNA – less closely related, less recent common ancestor.

  26. Making a Phylogenetic Tree • May use morphology, genetic and other data. • Typically “rooted” in a common ancestor. • Uses statistical analysis looking for “best fit”.

  27. Best Fit • Maximum parsimony – requires fewest DNA base changes or evolutionary events (Occam’s razor). • Branch lengths – suggest the closeness of the relationships and the time of branch points.

  28. Assignments • Read Chapter 26 or 16 in Hillis • Friday – today • Monday – Chapter 26 • Exam 3 -Tuesday

  29. Evolutionary History • Is in the organism’s genome. • Note – taxonomic relationships can be changed based on what the DNA tells us.

  30. Result • Taxonomy will become Genealogies, reflecting the organism’s "Descent with Modification“.

  31. Kingdom • Highest Taxonomic category in the Linnaeus system. • Old system - 2 Kingdoms 1. Plant 2. Animal

  32. 5 Kingdom System • R.H. Whittaker - 1969 • System most widely used, but is changing.

  33. Main Characteristics • Cell Type • Structure • Nutrition Mode • Problems in Kingdom Monera and Protista

  34. Current Views • Multiple Kingdoms – split life into as many as 8 kingdoms. • Domains – a system of classification that is higher than kingdom.

  35. 3 Domain System • Based on molecular structure for evolutionary relationships. • Prokaryotes are not all alike and should be recognized as two groups.

  36. 3 Domains 1. Bacteria – prokaryotic. 2. Archaea – prokaryotic, but biochemically similar to eukaryotic cells. 3. Eucarya – the traditional eukaryotic cells.

  37. Tree of Life

  38. Summary • What is Phylogeny? • What is a phylogenetic tree? • How is molecular data used in phylogeny? • Know the Domains and the Tree of Life.

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