Introduction into Drosophila Flashcards
Why is it useful to use a model organism that has been used many times before?
Lots of information of it (background knowledge) from previous studies
What are the advantages of using the drosophila as a model organism?
- Accessible embryology
- Accessible adult stages that are WELL DEFINED
- Low cost
- Fast generation time
- Excellent genetics
- No ethical concerns
What are the disadvantages of using the drosophila as a model organism?
Not a vertebrate (lacks features of a vertebrate)
Kept as live stocks
Describe the life cycle of the drosophila
1) Fertilised egg undergoes cleavage –> syncytial blastoderm
2) Gastrulation - form embryo with 3 layers \
3) Embryo hatches - first instar larvae
4) 2nd instar larvae
3) 3rd instar larvae
4) Larvae to pupa
5) Metamorphosis to adult fly
How long after fertilisation does it take the drosophila egg to become a syncytial blastoderm?
3 hours
What does the drosophila larvae contain/do?
Contains many digestive organs, gut and glands
Builds up energy sources
When does the larvae become pupa?
6-7 days after laying
What happens during the larvae to pupa stage?
Skin hardens and larvae skin dissolves
Adult tissue comes out of the larvae and forms the adult body shell
Where is the adult body tissue of the fly made?
In the larvae
What does the energy stores laid down by the larvae help?
Helps to shape metamorphosis
What is fascinating about drosophila courtship?
It is the STRONGEST and most REPRODUCIBLE behaviour
It is GENETICALLY ENCODED (how to act and respond)
Describe the structure of the drosophila penis
Tip of the testies contains the HUB
Hub is surrounded by STEM CELLS
What do the stem cells do in the drosophila penis?
What happens at the same time?
They divide
Each time divide:
- Cell closest to the hub maintains STEM CELL fate
- Cell furthest away DIFFERENTIATES into a CYST
What does the cyst in drosophila give rise do?
Cluster of spermatids
How does the cell closest to the hub maintain stem cell fate?
The hub secretes factors that maintain the fate:
- Unpaired
- JAK/STAT pathway
What do the ovaries of drosophila contain?
What are these?
Ovarioles
Where the egg develops from a stem cell
When are drosophila eggs fertilised?
How?
Immediately before they are laid
By sperm that is stored in the SEMINAL RECEPTACAL
Describe the structure of ovarioles
‘Time line’ of egg development in egg chambers:
- Start with stem cells that are maintained with JAK/STAT signalling
- Cells leave stem cell niche to start to differentiate
- These cells form a group of cells that ultimately give rise to a group of cells where one will become the EGG and the other will become the NURSE CELLS
What are ‘nurse cells’?
How do they do this?
Support cells that nurture and feed the egg (with yolk, proteins)
Do this by duplicating their DNA massively in order to make the supplies (maternal cotributions)
What are polytene chromosomes?
When do they occur?
What do you end up with?
Giant chromosomes
Occur when the DNA is duplicated but isn’t separated into 2 separate cells
Occurs in the nurse cells many many times
End up with MANY sets of DNA lying parallel to each other
How are the maternal contributions of the nurse cells moved into the developing egg?
Through cytoplasmic dumping through ring canals
What are ring canals?
Physical holes between the nurse cells and the egg
What happens do the nurse cells once they have performed cytoplasmic dumping?
They shrivel up and die
How are some maternal factors localised?
Actively by microtubule transport
What is the structure of the egg?
Chorion (egg shell)
Vitelline membrane (underneath the chorion)
What is the function of the vitelline membrane?
It is hydrophobic - prevents the egg from drying out
Where is the chorion secreted from?
Follicle cells
What happens once the egg is laid?
1) Pronuclei fuse to make a diploid organism
2) Nucleus formed divides 14 times (WITHOUT CELL DIVISION)
3) After the 14th division - the nuclei move to the outside of the cell and pauses
4) Membranes grow up from the outside into the yolk and forms many cells
How do the nuclei undergo 14 divisions without cell division?
Using the materials laid down by the mother in the nurse cells
