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Chapter 9 - Axis specification in Drosophila • Drosophila genetics is the groundwork for _______________l genetics • Cheap, easy to breed and maintain • Drosophila geneticists take pride in being __________, in ___________ information and being Mac users. • Problems- fairly complex, non-transparent Fig. 8.1 1. Cleavage Drosophila • Insects tend to undergo ________________cleavage occurs at _____ of the egg • In contrast to other creatures, insects form nuclei, then ____ ________ Termed a __________ _______ • Mitotic divisions #1-#9 - duplicate _____ (8 min/division) • Mitotic division #10 – nuclei _______ to rim • Mitotic division #11-14 – progressively _________divisions Fig. 9.1 1 7 10 1. Cleavage Drosophila • Mitotic divisions #14 – cells created with each nuclei to create the _______ _____________ 14 Note – each nuclei has a _________ of cytoskeletal proteins Nuclei staun Egg plasma membrane _____ between nuclei to create individual _____ Cycle 11-14- ______ ___________nuclear division slows and __________ increases Fig. 9.3 Tubulin stain 2. Gastrulation Ventral Dorsal Ventral furrow (from mesoderm) Fig. 9.6 Segments Head 3 _____ 8 _________ It becomes the ventral tube Fig. 9.7 2. Gastrulation Establishment of anterior-posterior polarity- Gene family Protein gradients rule the day Examples a. _______________in specific region of egg bicoid ____ caudel b. _____-among 1st gene transcribed in embryo Kruppel _________ c. ______ – result in 7 bands fushi tarazu ______ d. ____________ – result in 14 segments _______ wingless Fig. 9.8 2. Gastrulation a. Maternal effect genes Active during creation of _________________ _____ mRNA injected in anterior Caudel (diffuse) _______ mRNA injected, localize to posterior Hunchback (diffuse) Fig. 9.10 Bicoid prevents ____ mRNA _____________ Nanos prevents_________ mRNA ___________ a. Maternal effect genes Oocyte ________ Caudel and hunchback mRNA Mechanism Anterior _____ ______ mRNA mRNA Syncytial Blastoderm _______ Posterior Fig. 9.11 a. Maternal effect genes What if we mess up the ______gradient? Wildtype Fig. 9.14 Bicoid Inject bicoid into: Bicoid-/- Bicoid-/- Wild-type Anterior Middle Posterior mutant Two ____ Two _________ Head in ____ ____ Thus, bicoid specifies _______ development How does nanos specify __________? Answer- By preventing _________ translation Mechanism In anterior, ________ binds 3’UTR (untranslated region) of hunchback mRNA, and mRNA is polyadenylated and translated Anterior (no nanos) Posterior (with nanos) In posterior, nanos prevents _____________, and thus prevents ____________ Fig. 9.16 2. Gastrulation Segmentation genes Two steps in Drosophila development ____________ genes a. __________ ________ genes Egg Specification (Cell fate is flexible) Bicoid, nanos, hunchback, caudel, etc. Determination (Cell fate is determined) b. Gap genes c. ________ genes d. Segment polarity genes Maternal effect genes activate ____ genes, which activate _________ genes, which activate ________________ genes Segmentation genes establish ___________ Gap Pair-rule Fig. 9.19 Segment polarity a. Gap Genes Gap • Gap genes respond to ________ _______ proteins • Gap proteins interact to define specific________ of embryo • Four major gap proteins_______, ________, ________, _______ •These are all _____________ proteins- activate or repress ______________ hunchback giant kruppel knirps Fig. 9.21 b. Pair-rule genes • Gap genes activate and repress ___________ genes in ________ stripe, resulting in ________ stripes • Three major pair-rule proteins- ______, _____________, ______ •These are all ____________ proteinsactivate or repress transcription •Cells in each ______________contains • a unique ______ of pair rule genes expression unlike any other parasegment Fig. 9.21 Pair-rule b. Pair-rule genes Why do we observe expression of pair-rule proteins in ______________ segment? Pair-rule Answer- pair-rule genes use different ________ elements Example- even-skipped (a pair-rule gene) has several _______, but only one is _________ in a given stripe This ________ is only active in stripe #1 Different concentrations of ____ proteins determine _________ gene expression Fig. 9.22 c. _________ __________ genes Maternal, gap and pair-rule genes operate ______ cells are formed Pair-rule _____________________ 14 Fig. 9.1 Segment polarity Segment polarity genes act once cells are _______ c. Segment polarity genes Segment polarity genes encode proteins that make up ________ and __________ signal transduction pathways One cell produces ________ The adjacent cell produces ________ Fig. 9.25 Wingless and hedgehog activate expression of _________ indirectly 2. Gastrulation _______ _______ genes Responsible for directing structure formation of each segment • These genes are clustered on chromosome 3 in the ________ ___________ (also called Hom-C) in two regions• The _______________ complex• The ________________ complex- 1. The _____ of these genes on the chromosome matches order of ______________ expression 2. _____________ are regulated by all gene products expressed ___________ to it Chromosome 3 What about ______________ polarity?? • This occurs _______cells are created (post syncytial blastoderm) •______ ( a transcription factor) gradient is established •Dorsal is found throughout syncytial blastoderm, but only in _______ of ______cells How does this occur? By a very complex pathway involving _____ and __________ proteins ( and a host of other proteins) Organs form at the ___________ of dorsal-ventral and ____________ regions of gene expression