Drosophila Flashcards
(39 cards)
Define a morphogen.
A compound that, in varying concentrations, can cause cells to differentiate. The same molecule can produce various cell types depending on concentration.
What kind of information does a morphogen convey to a cell?
Positional.
Explain Wolpert’s French Flag model.
There are source (high) and sink (low) levels of morphogen at opposite ends of the organism. This creates a gradient across the embryo. Cells respond in strength accordingly, i.e. highest conc. of morphogen gives the strongest response etc.
In which organism was the first ever morphogen discovered?
Drosophila.
What is the drosophila ovary called?
The ovariole.
How many eggs does the ovariole produce everyday?
~100, regardless of prospective fertilisation.
What are the oocytes formed from?
Multipotent stem cells.
In oocyte formation, is cleavage asymmetric or symmetrical?
Asymmetric.
What happens to the oocyte at the 16-cell stage?
15 of the cells become nurse cells and 1 continues as the oocyte.
What do the nurse cells do?
Feed the oocyte.
What connects the nurse cells and oocyte?
Cytoplasmic ridges
What does the follicle cell do?
Produces the shell around the egg.
What happens to the nurse cells further in to development?
They transfer all the RNA and yolk proteins to the oocyte and shrivel up and die.
What kind of cleavage does the embryo undergo? What happens?
Superficial: only the nuclei cleave at first, there is no cleavage of cells. This forms syncytial blastoderm. The nuclei then migrate to the surface and cellularisation occurs.
How is the drosophila endoderm formed?
Furrows at the anterior and posterior ends of the embryo invert to form the endoderm.
How is the drosophila mesoderm formed?
The ventral furrow forms the mesoderm.
What happens in germ-band extension?
During the formation of the germ layers the tail flexes up over the head and back.
How long does it take for the larvae to hatch after the eggs are laid?
~24 hours.
What do the larval cuticular denticles indicate? Why is this useful?
Internal segmentation. This is useful in experiments: scientists create mutants to deduce the function of segment genes which are visible from the surface.
Define an egg polarity gene.
Genes that are expressed in gradients and specify the AP axis across the syncytium.
There are various types of egg polarity gene. What are the 3 main mutants?
- Anterior: have no head
- Posterior: have no abdomen
- Terminal: have no telson
What is arguably the most important anterior gene?
Bicoid is a nuclear transcription factor.
Bicoid RNA is anteriorly localised, although it diffuses across the embryo following the FF model.
What do bicoid mutants lack?
Anterior segments.
What is an important posterior gene?
Nanos.
