drosophila- setting up the body axes Flashcards
what did Thomas hunt Morgan establish
-drosopohila as a genetic model organism
how are we humans similar to flies
-Genes that control development of the fly, are very similar to genes that control the development of vertebrates including Human
-Evolution reuses and adapts genes and principles rather than invent new ways
-This means that by understanding developmental principles in the fly, we can learn about our own development
Why do we know so much about fly development?
-Christiane Nüsslein-Volhard Eric Wieschaus
-Christiane realized that Drosophila genetics could be applied to find genes controlling development. A simple but brilliant idea: they if are mutated they should lead to developmental defects that illustrate their function: FORWARD GENETICS
-“A mutation in a gene required for wing development should lead to wingless animals”
how is forward genetics described
- Mutant=>Function known…gene sequence needs to be determined Positional identification/cloning
-phenotype-> gene X
how is reverse genetics described
-Gene sequence known, Gene function needs to be determined
-gene X -> phenotype that we dont know
what does saturation screening do
-looks for or developmental mutants on a massive scale
-feed them with chemicals that damages DNA, changes the code and therefore leading to mutant
-In order to make a mutation a chemical (EMS) was used which acts at RANDOM
-This treatment was adjusted such that an average gene would be
destroyed with a chance of ~1/500
-So if there is ONE gene that is specifically required to form a wing and you search
1 line……..0.2% chance of finding it 10……2%
100….19%
500…. 64%
1000…87.5% 2000…98%
how did saturation screening work
-Mutated genes need to be homozygous to show their phenotype
-X 1000s
-An important part of the innovation, was developing methods for keeping and screening eggs from 1000s of lines very efficiently.
what did the basic mutant screens lead to
1) Basic understanding of how genes arec ontrolling the elaboration of a body plan
2) Molecular identification of many new genes and cell-to-cell signalling
pathways
3) Confirmed“Genetics”as a extremely powerful way to dissect biological processes
why did principles and genes identified, and methods employed help drive the understanding of processes in humans
-Soon after their discovery, it became clear very similar genes and principles were acting in other animals, including us, HUMANS.
-These genes are not just important during development but often remain important throughout life in
Homeostasis, Cancer, Regeneration, and Aging
what’s the Drosophila melanogaster life cycle
-short life cycle
-fertilised egg -> cleavage -> syncytial blastoderm -> gastrulation -> embryo -> hatching -> 1st 2nd and 3rd instar (larva) -> pupa -> metamorphosis -> adult fly
what do drosophila embryos initially develop as
- syncytium this is really important later, when the A/P axis is setup
-Syn=united, cytium=cell
-@ 3 hours post fertilization the embryos consists of a single layer of cells enclosing the yolk (containing a few nuclei). At the posterior of the embryo the POLE CELLS are separated off: these will form the GERM LINE.
time stamp of drosophila life cycle
-30 minutes: fusion of sperm and egg nuclei
-70 minutes: nuclear division creating syncytium
-90 minutes : nuclei migrate to periphery of cytoplasm
-2 hours : syncytial blastoderm
-3 hours : cellular blastoderm
cell fate
-once a cell has been specified to one of these fates—mesoderm, ectoderm, or endoderm all descendent will adopt that fate
-Ectoderm – Epidermis, Nervous sytem
Endoderm – Gut
-Mesoderm - Muscle
how do male and female drosophila differ
-different ends
-female = striped
-male = black
whats the screening stage
-Each end of the larva has unique structures, each segment has a chracteristic pattern of denticles. Denticles have a particular orientation this allows recognition of Anteroposterior polarity in each segment
-the dorsal side is different from the ventral side
