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Chapter 26 Phylogeny and the Tree of Life
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Phylogeny Phylon = tribe, geny = genesis or origin
The evolutionary history of a species or a group of related species.
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Phylogeny Found in the fossil record, molecules and genomes.
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Systematics The study of biological diversity and classification.
Uses evidence from the fossil record and other sources to reconstruct phylogeny.
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Systematics fuses: 1. Phylogeny- tracing of evolutionary relationships. 2. Taxonomy- the identification and classification of species.
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Taxonomy Natural to humans.
Modern system developed by Linnaeus in the 18th century.
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Linnaeus Taxonomy 1. Binomial Nomenclature – two names for each organism. Ex - Homo sapiens 2. Hierarchical System – arranges life into groups Ex - Kingdom Species: List
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Scientific names Composed of Genus and species.
Written in Latin and shown in italics or underlined. Governed by a set of rules and procedures.
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Goal of Systematics To have Taxonomy reflect the evolutionary affinities or phylogeny of the organisms.
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Phylogenetic Tree Branching diagram showing evolutionary relationships between organisms.
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Phylogenetic tree - Example
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Trees show: Ancestral lineage Branch points or nodes
Length of branch point suggests “time” and degree of closeness.
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Phylogenetic tree - Example
Branch point Ancestral Lineage
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Ideal Situation Monophyletic Grouping - a single ancestor gave rise to all species in the taxon.
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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.
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Problem Not all “likeness” is inherited from a common ancestor.
Problem is of homology vs analogy.
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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
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Convergent Evolution When unrelated species have similar adaptations to a common environment. A specific example of Analogy. Ex: Sharks and dolphins
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Only one is a cactus
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Need Methods to group organisms by similarities and phylogenies.
One possible method is Molecular Systematics.
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DNA patterns If similar DNA – more closely related, more recent common ancestor. If different DNA – less closely related, less recent common ancestor.
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Making a Phylogenetic Tree
May use morphology, genetic and other data. Uses statistical analysis looking for “best fit”.
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Best Fit Maximum parsimony – requires fewest DNA base changes.
Branch lengths – suggest the closeness of the relationships and the time of branch points.
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Result Taxonomy will become Genealogies, reflecting the organism’s "Descent with Modification“.
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5 Kingdom System R.H. Whittaker - 1969
System most widely used, but is changing.
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Main Characteristics Cell Type Structure Nutrition Mode
Problems in Kingdom Monera and Protista
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Current Views Multiple Kingdoms – split life into as many as 8 kingdoms. Domains – a system of classification that is higher than kingdom.
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3 Domain System Based on molecular structure for evolutionary relationships. Prokaryotes are not all alike and should be recognized as two groups.
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3 Domains 1. Bacteria – prokaryotic.
2. Archaea – prokaryotic, but biochemically similar to eukaryotic cells. 3. Eukarya – the traditional eukaryotic cells.
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