Introduction into Drosophila

Question 1

Why is it useful to use a model organism that has been used many times before?

Answer 1

Lots of information of it (background knowledge) from previous studies

Question 2

What are the advantages of using the drosophila as a model organism?

Answer 2

• Accessible embryology
• Accessible adult stages that are WELL DEFINED
• Low cost
• Fast generation time
• Excellent genetics
• No ethical concerns

Question 3

What are the disadvantages of using the drosophila as a model organism?

Answer 3

Not a vertebrate (lacks features of a vertebrate)

Kept as live stocks

Question 4

Describe the life cycle of the drosophila

Answer 4

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

Question 5

How long after fertilisation does it take the drosophila egg to become a syncytial blastoderm?

Answer 5

3 hours

Question 6

What does the drosophila larvae contain/do?

Answer 6

Contains many digestive organs, gut and glands

Builds up energy sources

Question 7

When does the larvae become pupa?

Answer 7

6-7 days after laying

Question 8

What happens during the larvae to pupa stage?

Answer 8

Skin hardens and larvae skin dissolves

Adult tissue comes out of the larvae and forms the adult body shell

Question 9

Where is the adult body tissue of the fly made?

Answer 9

In the larvae

Question 10

What does the energy stores laid down by the larvae help?

Answer 10

Helps to shape metamorphosis

Question 11

What is fascinating about drosophila courtship?

Answer 11

It is the STRONGEST and most REPRODUCIBLE behaviour

It is GENETICALLY ENCODED (how to act and respond)

Question 12

Describe the structure of the drosophila penis

Answer 12

Tip of the testies contains the HUB

Hub is surrounded by STEM CELLS

Question 13

What do the stem cells do in the drosophila penis?

What happens at the same time?

Answer 13

They divide

Each time divide:

• Cell closest to the hub maintains STEM CELL fate
• Cell furthest away DIFFERENTIATES into a CYST

Question 14

What does the cyst in drosophila give rise do?

Answer 14

Cluster of spermatids

Question 15

How does the cell closest to the hub maintain stem cell fate?

Answer 15

The hub secretes factors that maintain the fate:

• Unpaired
• JAK/STAT pathway

Question 16

What do the ovaries of drosophila contain?

What are these?

Answer 16

Ovarioles

Where the egg develops from a stem cell

Question 17

When are drosophila eggs fertilised?

How?

Answer 17

Immediately before they are laid

By sperm that is stored in the SEMINAL RECEPTACAL

Question 18

Describe the structure of ovarioles

Answer 18

‘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

Question 19

What are ‘nurse cells’?

How do they do this?

Answer 19

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)

Question 20

What are polytene chromosomes?

When do they occur?

What do you end up with?

Answer 20

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

Question 21

How are the maternal contributions of the nurse cells moved into the developing egg?

Answer 21

Through cytoplasmic dumping through ring canals

Question 22

What are ring canals?

Answer 22

Physical holes between the nurse cells and the egg

Question 23

What happens do the nurse cells once they have performed cytoplasmic dumping?

Answer 23

They shrivel up and die

Question 24

How are some maternal factors localised?

Answer 24

Actively by microtubule transport

Question 25

What is the structure of the egg?

Answer 25

Chorion (egg shell)

Vitelline membrane (underneath the chorion)

Question 26

What is the function of the vitelline membrane?

Answer 26

It is hydrophobic - prevents the egg from drying out

Question 27

Where is the chorion secreted from?

Answer 27

Follicle cells

Question 28

What happens once the egg is laid?

Answer 28

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

Question 29

How do the nuclei undergo 14 divisions without cell division?

Answer 29

Using the materials laid down by the mother in the nurse cells