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Chapter 25 Phylogeny and the Tree of Life

Chapter 25 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 25 Phylogeny and the Tree of Life

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  1. Chapter 25Phylogeny 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.

  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. Goal of Systematics • To have Taxonomy reflect the evolutionary affinities or phylogeny of the organisms.

  10. Phylogenetic Tree • Branching diagram showing evolutionary relationships between organisms.

  11. Phylogenetic tree - Example

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

  13. Phylogenetic tree - Example Branch point Ancestral Lineage

  14. Question? • How to group taxa so that the phylogenetic relationships are correct ?

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

  16. 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.

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

  18. 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

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

  20. Only 1 is a mole

  21. Only one is a cactus

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

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

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

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

  26. Best Fit • Maximum parsimony – requires fewest DNA base changes. • Branch lengths – suggest the closeness of the relationships and the time of branch points.

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

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

  29. Kingdom • Highest Taxonomic category • Old system - 2 Kingdoms 1. Plant 2. Animal

  30. 5 Kingdom System • R.H. Whittaker - 1969 • System most widely used, but is changing.

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

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

  33. 3 Domain System • Based on molecular structure for evolutionary relationships. • Prokaryotes are not all alike and should be recognized as two groups.

  34. 3 Domains 1. Bacteria – prokaryotic. 2. Archaea – prokaryotic, but biochemically similar to eukaryotic cells. 3. Eucarya – the traditional eukaryotic cells.

  35. 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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