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Arrows point to the mouse jaw and the mouse hindlimb

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Unformatted text preview: Freshwater sCcklebacks have a mutaCon in one of the regulatory segments d. Freshwater sCcklebacks have a series of mutaCons in mulCple regulatory segments 3 4/11/13 In freshwater s=cklebacks, the pitx1 gene is unchanged, but the regulatory region that controlled expression in the pelvis is mutated Pitx1 is no longer expressed in pelvis, so pelvic spines cannot form Other vertebrates also have a pitx1 gene, normally active in the jaw and hindlimb, just like in sticklebacks normal mutant At le< is a mouse embryo. Arrows point to the mouse jaw and the mouse hindlimb. In mouse knockout (or knockdown), lack of pitx1 gene means no protein, no func=on of pitx1 in all regions: prevents both jaw and hindlimb from forming Picture on le< is normal mouse Picture on right (no jaw and no hindlimb) is: a. Mouse with loss of func=on muta=on in coding region of pitx1 b. Mouse with gain of func=on in coding region of pitx1 c. Mouse with muta=on in regulatory segment of pitx1 “Deep Homology” When not only structures are homologous, but whole paYerns of development (transcrip=on factors and signaling molecules) are Homologous Many examples! Sea urchin fly Micromeres are the “organizer” 4 4/11/13 Move the micromeres, and they induce another set of skeletal structures on the other side AND, the micromeres express β ­catenin Other distantly related animals: insects (Drosophila) Drosophila gastrula=on Looks like sea urchin Looks like vertebrates with axes flipped Cells that ini=ate gastrula=on have beta catenin Next stage: determining the cells that will be part of the nervous system (Drosophila) Stage 8 Establishment of embryonic CNS in Drosophila: Notch/Delta Clusters of proneural (7 cells) single neuroblasts SAME MOLECULES, DIFFERENT AXES! Stage 9 from Campuzano and Modolell, 1992 Evolu=on of the Eye: all eyes derived from a common ancestor? Or did they evolve separately? (analogous rather than homologous) Later structures? Camera ­type eye of an owl. Mirror ­type eye of a scallop Compound eye of a horsefly. Prototypic eye in planarian: a single photoreceptor cell and a pigment cell Gehring 2005 5 4/11/13 Is ther...
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