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DB8notes - BIOLOGY 205/SECTION 7 DEVELOPMENT LILJEGREN...

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BIOLOGY 205/SECTION 7 DEVELOPMENT- LILJEGREN Lecture 8 Development of the Fruit Fly Drosophila 1. The fruit fly- a highly successful, specialized organism a. Quick life cycle includes three larval stages and a metamorphosis. Spends only 1 day as an embryo b. Body plan built from a repeated set of units: segments . Sets of genes control development in segmented animals (including us) by specifying and refining segment fates. i. Each segment has unique identity! ii. Head 3 segments. Thorax- 3 segments. Abdomen-8 segments. iii. True for maggot and adult. 2. Why flies? a. Lots of reasons we talked about the first day of class: small, sequenced genome, many genetic and molecular tools, small and cheap. b. Very reproducible anatomy- every hair same from one fly to next, and can see segmentation on outside of body c. Anatomical, developmental, & even behavioral similarities to vertebrates. Adult flies do many things that we do - they eat, sleep, learn, have sex etc. So these processes can be genetically analyzed in flies. d. Primary reason- History i. In early 1900s when science of genetics rediscovered, Thomas Hunt Morgan chose fruit fly to study genetics. He was one of first scientists to systematically isolate "mutations" affecting visible traits (at first just found naturally occuring mutations). A “mutant” is an animal lacking the product of single gene. The first fly mutant found in 1910 was the white mutant. 1. Normal, wild-type flies have eyes containing red pigments that protect vision. 2. Found mutant fly with white eyes. 3. White gene encodes a transmembrane channel protein that pumps pigment precursors into cells. It turns out that it’s a member of a large family of channel proteins. 4. Related to a human gene that when mutated causes cystic fibrosis ! This related CFTR protein is a transmembrane channel protein that moves chloride ions. ii. Thousands of mutations have now been identified that affect all aspects of body structure/function. Christiane Nüsslein-Volhard and Eric Wieschaus set up a huge screen to look for developmental mutants that affect the body plan of fruit flies - they got lots of mutants and a Nobel prize! The analysis of these mutations has increased our knowledge of development dramatically. e. Today, we’re going to talk about some of the keys stages of embryonic development and pattern formation in the fly—remember that the fly’s body plan is assembled in 24 hours!
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3. The Maternal Effect Genes Establish the Anterior-Posterior axis early in development. a. These genes, like bicoid and nanos, are mRNAs made by nurse cells and pumped into the oocyte through cytoplasmic bridges. They form gradients which set up the Anterior-Posterior axis. The proteins are mostly transcription factors that activate GAP GENES (see below).
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