466n_Lectures_24-27_white - 162 Animal Development and...

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Unformatted text preview: 162 Animal Development and Evolution FIRST - WHICH GENES AFFECT MORPHOLOGY? LATER - WHAT ROLES HAVE CHANGES IN THE NUMBER, REGULATION AND FUNCTION OF THESE GENES PLAYED IN EVOLUTION? 163 Key Concepts of Embryology Were Established by Manipulating Embryos and Tissues • Organizers – regions that have long range effects on the fate of surrounding tissues • dorsal lip of amphibian egg • parts of limb bud • Morphogens – substances postulated to induce different responses by cells in concentration-dependent manner Before Genetics 164 Organizers in Animal Embryos 165 CONSIDER: The isolation of the gene products responsible for organizer or morphogen activity was a daunting, if not impossible, task. Biochemists failed completely for more than 50 years. KEY ADVANCE - USE GENETIC APPROACH • Pick a species that is • small • has rapid life cycle • well studied • Combine the above with powerful molecular cloning techniques • We now know more about development than was imaginable 25 years ago 166 A Geneticist's View of Development • Which genes are important for Pattern Formation ? • Where and when are these genes active? • How are they regulated? • Through what mechanisms do they influence animal form? 167 The Workhorses: • Why the Fly? – outstanding cytogenetics – good model of highly advanced animal • The Worm? – well studied cell lineage – good genetics – small genome Fruit Fly - Drosophila melanogaster Nematode Worm - Caenhabditis elegans 168 Life Cycle of Fruit Fly 169 Some very interesting genes had already been identified (Efforts of E.B. Lewis 1940-1980) These caused interesting adult phenotypes ( homeotic ) e.g., • mutants in Bithorax Complex flies with 2 pairs of wings instead of one. • Antennapedia mutants exhibit legs in place of antennae Most of these phenotypes in adults are dominant , resulting from changes in gene regulation. 170 normal bithorax mutant Antennapedia 170 normal bithorax mutant Antennapedia mutant 171 Homeotic Genes 1) Mutants transform one segment into another: e.g. Antenna Leg T3 Hindwing T2 Forewing i.e. they affect segment identity 2) Found in gene complexes 3) Order of genes on chromosome corresponds to order of segments influenced. 4) These genes regulate fate of entire segments and body regions. 172 Homeotic (Hox) Regulate Identity of Body Parts in the Adult… . 173 AND Homeotic (Hox) Regulate Identity of Body Parts in the Embryo So, Where and When are Hox Genes Active ? 174 Mutation in a single gene 1. brute force, physical mapping 2. transposon tagging 3. homology to already cloned gene DNA (genomic) cDNA Probe library of appropriately staged cDNA made from nRNA Insert into plasmid or phage vector such that efficient translation is possible in situ hybridization bacteria protein rabbits antiserum grow inject bleed localize protein in prepared tissues (embryos, eggs, dissected organs, etc.) in situ immuno- histochemistry How Do We Find Out Where a Gene is Expressed?...
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This note was uploaded on 03/26/2010 for the course GENETICS 466 taught by Professor Staff during the Fall '08 term at University of Wisconsin.

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466n_Lectures_24-27_white - 162 Animal Development and...

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