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Lecture 4

Phylogeny, origin and diversity of eukaryotes (Lecture 4)

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Biology (Sci)
BIOL 111
Irene Gregory- Eaves

Biology Lecture 4 Phylogeny, origin and diversity of eukaryotes 9/13/2011 6:43:00 AM Pre-lecture vocabulary  Taxon/taxa  Taxonomy  Phylogeny  Mitosis  Meiosis  Haploid  Diploid Taxonomy  The classification of life forms  Two key ideas: 1. binomial nomenclature (two names) - genus species (a group of closely related species) - Example: homo sapiens - when writing we use italics or underlined 2. Hierarchy Kingdom, phylum, class, order, family, genus, species “Kings Play Chess On Finely Grained Sand” - Example of hierarchy of Humans: Animalia, Chordata, Mammalia, Primate, Hominidae, Homo, sapiens  Today we use a 3 domain system: Bacteria, Archaea, Eukarya How to read a phylogenetic tree (Vocabulary)  The position of the branches could be rotated around the node and won’t change the meaning of the tree Analogy vs. homology  Homology: similarity due to common ancestor - Example: Bat wing and human arm—similar because the bone structure evolved in a common ancestor  Analogy: similarity due to common environment (convergent evolution) - Example: Bird wing and insect wing—similar because each evolved wings from different wingless ancestors to solve the problem of flight Bird wing and bat wing however are both: the bones are homologous and the wings are analogous How to build a phylogeny  Step 1: get a list of observable “traits” or “characters” for each taxon (genetic data)  Step 2 (optional): identify order of progression on traits (jaw came after no jaw) and need to be looking at homologous traits  Step 3: let a computer find groupings, trying to find monophyletic groupings—the most parsimonious tree (simplest) Taxon vs. Clade: FIND DEFINITIONS A monophyletic group: ancestor and all its descendants 1. Taxonomy & phylogeny Derived Trait: trait shared by the group but not found in their ancestor  This means that they evolved to get that trait 3. Diversity of “protists” 35 Taxonomy and Phylogeny summary:eded  As we learn more, ideas about taxonomy have changed, but still use binomial nomenclature the origin of eukaryotes? system  Phylogenies are based on evolutionary history and strive to form monophyletic groups  Similarities in morphology are not necessarily due to a common ancestor—not always A. origin of 43% 43% homologous  Still in a state of flux B. formation of O 2 Which event preceded the origin of eukaryotes? The formation of oxygen availability in the atmospheatmosphere C. A & B 14% .. .. B ml oO A& inf atn oi fr 36 Eukaryotes—true nucleus  Most life we are familiar with and can see are eukaryotes (i.e., animals, plants, fungi, algae)  Evolved 1-2 billion years old  Differ from prokaryotic ancestors: - no cell wall or a non-peptidoglycan cell wall - have membrane-enclosed organelles (e.g. nucleus, mitochondria, chloroplasts), larger ribosomes  How they evolved from a prokaryote: 1. Lose the cell wall, it became more flexible 2. Infolding of the membraneincreased surface area and allowed bigger cells to grow 3. Form vacuoles by pinching of membrane that evolved to have different roles 4. DNA and ribosomes are already attached to membrane; more infolding until they’re surrounded nucleus and endoplasmic reticulum (ER) 5. Build cytoskeletonmicrotubules and microfilaments which allow things to move inside the cell and for the cell to move 6. Extend cytoskeleton into flagellum and develop motion 7. Develop phagocytosis the process of one cell engulfing another particle or cell 8. Swallow a proteobacterium evolution of mitochondria 9. Optional: swallow a cyanobacterium chloroplast Endosymbiosis: “internal and living together”  One cell “swallows” a prokaryote but ends up living together instead of being digested  Over long time living together - Genome of endosymbiont becomes very reduced, may move to the nuclear genome  Evidence: - Double cell membrane around mitochondria like you would see in a protyobacterium - Genes in mitochondria that match bacterial genes - Mitochondria and chloroplasts reproduce by binary fission and they can do this independent of cell Eukaryotes: monophyletic group, all descendants are from a common ancestor and it includes animals, plants, and fungi as well as many protists Protists: a term used out of convenience, not a taxonomic group  Eukaryotes that are not plants, fungi, nor animals  Size: microscopic to meters long  Photoautotrophs, (chemo)heterotrophs  Niches: free-living, endosymbionts, parasites  Diverse methods of locomotion Diversity in Protists: many groups Unikonts: “single cone”  Referring to single flagell
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