Bio171-F08-lec35 - Lecture 35: Monday November 24, 2008...

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Unformatted text preview: Lecture 35: Monday November 24, 2008 Biology 171 Todays Topic: Evolution of Metazoan Development Announcements Development and Evolution Revisit Deuterostome & Protostome Dev. Indeterminate & Determinate Development Transcription Factors - Their Key Roles Body Patterning in the Drosophila Model System Role of Hox Genes in Bilaterian Evolution Microevolution in Stickleback sh Next Week in Discussion: Human Diversity No Class Wed. Nov. 26 Text Reading Lec 35 : 2 nd ed: Chapter 22 (469-489) 3 rd ed: Chapter 21 (434-448) Lec. 36: 2 nd ed: Chapter 55 (1272-1281) 3 rd ed: Chapter 55 (1249-1260) Development is a process by which an organism successively takes on the different body forms that constitute its life cycle. This process is ongoing throughout the life cycle of the organism and only ceases with its death. Because developmental programs are genetically programmed, they can mutate and evolve over time. Modifications of ancestral developmental pathways have produced the great diversity in animal body plans we see in nature. Development & Evolution Most animals are members of the Bilateria : have bilateral symmetry and 3 developmentally distinct tissue layers. The major Division within the Bilateria is that of Protostome and Deuterostome Lineages. Protostomes differ from Deuterostomes in their early cell division (cleavage), and how their embryonic gut & internal body cavity (coelom) is formed They also differ in the Fexibility of their early developmental programs: how individual cell fates are controlled. Protostome Development is Determinate - the fate of each cell is fixed as it is formed - see nematode worm cell lineage below Remove a cell and the tissues/organs that cell (and its descendants) would normally form are missing from the developing embryo. Only the zygote is totipotent it can give rise to all other cell types. If a 2-cell or 4-cell deuterostome embryo is mechanically dissociated, individual cells are capable of forming a complete, but smaller, embryo if cultured in isolation. All of these cells are totipotent they can give rise to all other cell types. Deuterostome Development is Indeterminate Also called regulative development, cell fate is not Fxed, and can compensate for loss of other cells. Totipotency is a time dependent attribute in deuterostome embryonic cells, and it is progressively lost as cells become more differentiated during development....
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This note was uploaded on 01/30/2012 for the course BIO 171 taught by Professor Josephinekurdziel during the Fall '08 term at University of Michigan.

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Bio171-F08-lec35 - Lecture 35: Monday November 24, 2008...

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