Chapter 26 Phylogeny and the Tree of Life

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1 Chapter 26 Phylogeny 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 18 th 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


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

11 Phylogenetic Tree Branching diagram showing evolutionary relationships between organisms.

12 Phylogenetic tree - Example

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

14 Phylogenetic tree - Example Ancestral Lineage Branch point

15 Question? How to group taxa so that the phylogenetic relationships are correct?

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


18 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.


20 Problem Not all likeness is inherited from a common ancestor. Problem is of homology vs analogy.

21 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

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

23 Only 1 is a mole

24 Only one is a cactus

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

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

27 DNA patterns If similar DNA more closely related, more recent common ancestor. If different DNA less closely related, less recent common ancestor.


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

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

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


33 Result Taxonomy will become Genealogies, reflecting the organism s "Descent with Modification.

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

35 5 Kingdom System R.H. Whittaker System most widely used, but is changing.


37 Main Characteristics Cell Type Structure Nutrition Mode Problems in Kingdom Monera and Protista

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

39 3 Domain System Based on molecular structure for evolutionary relationships. Prokaryotes are not all alike and should be recognized as two groups.

40 3 Domains 1. Bacteria prokaryotic. 2. Archaea prokaryotic, but biochemically similar to eukaryotic cells. 3. Eucarya the traditional eukaryotic cells.


42 Tree of Life



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