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mouse. worm. Genetic Model Organisms. fish. yeast. fruit fly. weed. Drosophila melanogaster Genetics and Developmental Biology Physiology and Behavior Many disease-causing genes in humans have corresponding homologues in the fly genome Cancer Neurodegenerative disease
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mouse worm Genetic Model Organisms fish yeast fruit fly weed
Drosophila melanogaster Genetics and Developmental Biology Physiology and Behavior Many disease-causing genes in humans have corresponding homologues in the fly genome Cancer Neurodegenerative disease Drug addictions Diabetes Obesity
Life cycle of Drosophila • embryogenesis • three larval stages • a pupal stage • the adult stage
Groups of cells called imaginal discs are set aside at specific sites in the larval body. From these the various body parts develop during pupation (adult muscle, the nervous system, etc).
Advantages of the fly system • A relatively short life cycle (10 days) • Culturing flies is cost-effective (vs mice) • A variety of genetic and molecular tools available (functional testing in vivo) • Complete genome sequence (13,500 genes)
Advantages of the fly system • A relatively short life cycle (10 days) • Culturing flies is cost-effective (vs mice) • A variety of genetic and molecular tools available (functional testing in vivo) • Complete genome sequence (13,500 genes)
Thomas H. Morgan and the Caltech fly group • Bridges (left) and Sturtevant in 1920 • (B) Morgan in 1917
Christiane Nüsslein-Volhard, Eric Wieschaus and the Baden fly group (1980) Nüsslein-Volhard and Wieschaus (along with Edward Lewis) were awarded the 1995 Nobel Prize for Physiology/Medicine.
Saturation Mutagenesis Screen and the Segmentation Hierarchy
Biological question Screening assay Speed Specificity Lead to biological insight?
Drosophila embryogenesis 3 h pole cells (germ line) Cellular blastoderm Anterior Posterior 10 h Segmented embryo 22 h 1st instar larva
Segmentation Hierarchy Maternal genes Gap genes Pair rule genes Segment polarity genes
Molecular Mechanisms What is the gene product? Where and when is it active? Was the genetic prediction correct?
ftz (fushi tarazu) gene expression pattern in situ hybridization (RNA detection) need probe! Ernst Hafen and Walter Gehring (1983)
even-skipped (blue), ftz (red) antibody staining (protein detection) need antibody!
Gap Genes hunchback (blue) and Krueppel (green) Fluorescent staining
Molecular patterningof the embryo Bicoid (blue) Even skipped (red) Krüppel (yellow)
Biological question Screening assay Speed Specificity Lead to biological insight?
Germ-line Transformation and in vivo Genetic Manipulations
For example... Is the striped expression of ftz really necessary? What happens if you express ftz everywhere? How would you test this?
Transposase (“helper”) plasmid acts on P-element ends for integration into genome 2 transformation Heat shock promoter-ftz P-element plasmid 1 ftz Adapted from Wang and Lin, 2004
Syncitial blastoderm Germ cells Transposable P-element mediated transformation Allan Spradling and Gerald Rubin (1982)
Drosophila embryogenesis 3 h pole cells (germ line) Cellular blastoderm Anterior Posterior 10 h Segmented embryo 22 h 1st instar larva
The UAS-Gal4 System: How you can make flies with eyes on their legs
Gal4 x promoter Gal4 UAS gene Regulating Gene Activity with Pinpoint Precision progeny flies will express gene in the place of choice
wild-type Misexpression of eyeless using the UAS-Gal4 system
Polytene chromosomes Specialized chromosomes Discovered by Balbiany in 1881 in salivary gland of drosophila larva (3rd instars) Why salivary gland of drosophila larva will have Polytene Chromosomes????????????????
Drosophila Karyotype Drosophila Polytene chromosome
1933, Painter showed the banding pattern in Drosophila 1935, Bridges Banding pattern is fixed in a particular chromosome in a particular species
Polytene chromosome is found in 3rd instar larva of Diptera Also found in Malpighian tubules Mid Gut epithelium Rectum Of Diptera order of insects And in ovary of some plants
wildtype obese (leptin)