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25_Ward_Metazoa+Outline - Lecture 25(18 February 2011 2...

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BIS2C W2011 Lecture 25 (18 February 2011) 1 Introduction to Metazoa Broader context: the eukaryote tree Thus far among the eukaryotes we have considered (1) unicellular eukaryotes (heterogeneous group); (2) land plants; and (3) fungi. Review the main lineages of eukaryotes, and note the major multicellular clades: plants, fungi, and animals. Animals are part of a larger clade known as the opisthokonts . Choanoflagellates small group of aquatic heterotrophic eukaryotes some unicellular, others colonial (known reproduction is asexual) cells similar in structure to sponge choanocytes: collar of microvilli surrounding flagellum Features shared between Choanoflagellates and Metazoa 1. Collar cells 2. Structure of mitochondria 3. DNA sequence data 4. Homologues of metazoan cell signaling and adhesion genes Refs: Carr, M. (2008) Proc. Natl. Acad. Sci. USA 105:16641–16646. Ruiz-Trillo et al. (2008) Mol. Biol. Evol. 25:664–672. Metazoan features Feature Synapomorphy? Unique?
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Unformatted text preview: Lecture 25 (18 February 2011) 2 Major lineages of metazoans This phylogeny is in line with results from recent genomic studies, e.g.: Philippe, H. et al. 2009. Phylogenomics revives traditional views on deep animal relationships. Current Biology 19 :706–712. doi:10.1016/j.cub.2009.02.052 The older edition of the textbook ( Life, 8 th edition ) presents a different phylogeny in which sponges are paraphyletic – this has implications for inferring the ancestral features of metazoans. Organization of animal body plans Animal symmetry : arrangement of body parts Radial symmetry (multiple imaginary planes that divide the animal into equal halves) Bilateral symmetry (single plane divides animal into left and right mirror-image halves) Cephalization and segmentation Developmental patterns Zygote blastula gastrula Cleavage (e.g., radial or spiral) formation of blastula . Gastrulation : in-pocketing of blastula to form gastrula formation of cell layers...
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