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Chapter 26

Chapter 26. Phylogeny and the Tree of Life. What you need to know:. The taxonomic categories and how they indicate relatedness. How systematics is used to develop phylogenetic trees. The three domains of life including their similarities and their differences.

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Chapter 26

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  1. Chapter 26 Phylogeny and the Tree of Life

  2. What you need to know: • The taxonomic categories and how they indicate relatedness. • How systematics is used to develop phylogenetic trees. • The three domains of life including their similarities and their differences.

  3. Systematics: classifying organisms and determining their evolutionary relationships Taxonomy (classification) Systematics Phylogenetics (evolutionary history)

  4. Tools used to determine evolutionary relationships: • Fossils • Morphology (homologous structures) • Molecular evidence (DNA, amino acids) Who is more closely related? Animals and fungi are more closely related than either is to plants.

  5. Taxonomy: science of classifying and naming organisms • Binomial nomenclature (Genus species) Naming system developed by Carolus Linnaeus.

  6. REMEMBER!! • Dear King Philip Came Over For Good Spaghetti • Dominant Kings Played Canucks On Friday, Gretzky Scored!

  7. Phylogenetic Tree • Branching diagram that shows evolutionary history of a group of organisms

  8. Terminology • Branch Point- represents the divergence of 2 evolutionary lines • Sister taxa- groups of organisms that share an immediate common ancestor (closest relative) • Rooted- a branch point within the tree represents the most recent common ancestor of all taxa in tree • Extant- still living • Basal taxon- lineage that diverges early in history and lies on branch near common ancestor (G) • Polytomy- branch point where more than 2 descendant groups emerged

  9. 3 points about Phylogenetic Trees 1) Intended to show patterns of descent not phenotypic similarities Ex) Crocodiles most closely related to birds than lizards but look more like lizards

  10. 3 points about Phylogenetic Trees 2) Sequence of branching does not always indicate absolute age of species 3) Do not assume that a taxon on a phylogenetic tree evolved from the taxon next to it

  11. Leopard Turtle Hair Salamander • Clade= group of species that includes an ancestral species + all descendents • Can be nested within larger clades, but not all groupings or organisms qualify as clades • Shared derived characteristics areused to construct cladograms Amniotic egg Tuna Four walking legs Lamprey Hinged jaws Lancelet (outgroup) Vertebral column Cladogram

  12. Taxon is equivalent to a clade if it is monophyletic • Consists of an ancestral species and ALL its descendants

  13. Grouping 1 E J K D H G F C I B A (a)Monophyletic. In this tree, grouping 1, consisting of the seven species B–H, is a monophyletic group, or clade. A mono-phyletic group is made up of an ancestral species (species B in this case) and all of its descendant species. Only monophyletic groups qualify as legitimate taxa derived from cladistics. • A valid clade is monophyletic • Signifying that it consists of the ancestor species and all its descendants Figure 25.10a

  14. Paraphyletic Group • Consists of an ancestral species and some, but not all, of its descendants

  15. Grouping 2 G J K H E D C I F B A (b)Paraphyletic. Grouping 2 does not meet the cladistic criterion: It is paraphyletic, which means that it consists of an ancestor (A in this case) and some, but not all, of that ancestor’s descendants. (Grouping 2 includes the descendants I, J, and K, but excludes B–H, which also descended from A.) • A paraphyletic clade • Is a grouping that consists of an ancestral species and some, but not all, of the descendants Figure 25.10b

  16. Polyphyletic Group • Includes distantly related species but does not include their most recent common ancestor

  17. D E J G H K I F C B A (c)Polyphyletic. Grouping 3 also fails the cladistic test. It is polyphyletic, which means that it lacks the common ancestor of (A) the species in the group. Further-more, a valid taxon that includes the extant species G, H, J, and K would necessarily also contain D and E, which are also descended from A. • A polyphyletic grouping • Includes numerous types of organisms that lack a common ancestor Grouping 3 Figure 25.10c

  18. Monophyletic, paraphyletic, and polyphyletic groups

  19. Constructing a phylogenetic tree A “0” indicates a character is absent; a “1” indicates that a character is present.

  20. Branch lengths can represent genetic change

  21. Branch lengths can indicate time

  22. Draw a phylogenetic tree based on the data below. Draw hatch marks on the tree to indicate the origin(s) of each of the 6 characters.

  23. Answer:

  24. Various tree layouts Circular (rooted) tree Unrooted tree Rooted tree

  25. Principle of maximum parsimony: use simplest explanation (fewest DNA changes) for tree – “keep it simple” Occam's razor • Molecular clocks: some regions of DNA appear to evolve at constant rates • Estimate date of past evolutionary events • Eg. Origin of HIV infection in humans= 1930’s

  26. Tree of Life • 3 Domains: Bacteria, Archaea, Eukarya

  27. SYSTEMATICS focuses on phylogeny Biological diversity taxonomy cladistics classification Identification of species D K P C O F G S Homologous similarities fossils binomial molecular Genus, species morphology

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