Drosophila Eye Development

Question 1

What are imaginal discs?

Answer 1

Areas which develop into the mouth, eye etc

Question 2

When are imaginal discs set side?

Answer 2

In early embryogenesis

Question 3

What is the haltere?

Answer 3

A balance organ

Question 4

How many cells gather to form an imaginal disc?

Answer 4

Around 30

Question 5

How big do structures from imaginal discs grow?

Answer 5

To about 50,000 cells

Question 6

What is the phenotype of a Pax 6 mutant?

Answer 6

They have no eyes

Question 7

What is eyeless?

Answer 7

A homeobox transcription factor homologous to vertebrate PAX6

Question 8

Eyeless PAX6 is both … and … to make an eye

Answer 8

necessary

sufficient

Question 9

PAX6 misexpressed in a fly induces what?

Answer 9

An ectopic eye

Question 10

How many flies do drosophila have?

Answer 10

5 - 2 large and 3 small

Question 11

What are the flies small eyes called?

Answer 11

Ocelli

Question 12

What are ocelli used for?

Answer 12

Sense the flies orientation ie where they are in the sky

Question 13

Each large eye consists of how many ommatidia?

Answer 13

800

Question 14

What are ommatidia?

Answer 14

each of the optical units that make up the compound eye of an insect.

Question 15

Why are the ommatidia hexagonal?

Answer 15

Makes them efficient in their packaging

Question 16

Each ommatidia is associated with what?

Answer 16

A bristle involved in the cleaning process

Question 17

Why are the fly eyes curved?

Answer 17

To give them a wide plane of view

Question 18

Each ommatidia consists of:

Answer 18

8 photoreceptors
4 cone cells
2 primary pigment cells
6 secondary pigment cells
3 tertiary pigment cells

Question 19

Why do fly eyes contain red granules around the lens?

Answer 19

They stop light from other places being scattered so light is focused in a straight line on the ommatidia

Question 20

Why does a white mutant have worse vision than a wildtype fly?

Answer 20

The white mutant has no red granules so the light scatters and confuses things

Question 21

What are rhabdomeres?

Answer 21

Light sensitive structures
They trigger neuronal input
Made of microvilli packed with rhodopsin

Question 22

How many rhabdomeres are there?

Answer 22

7

Question 23

What is the role of the equator across the eye?

Answer 23

It senses the horizon

Question 24

Where do R1 to R6 axons project into?

Answer 24

The lamina

Question 25

Where do R7 and R8 photoreceptors project to?

Answer 25

The medulla

Question 26

Why can a single object be seen by many rhabdomeres?

Answer 26

It increases resolution

Question 27

What do flies respond to?

Answer 27

Movement

Question 28

When does most growth of the eye field occur?

Answer 28

The third instar

Question 29

Photoreceptors are preceded by what?

Answer 29

The morphogenetic furrow

Question 30

Describe the morphogenetic furrow

Answer 30

Rich in actin
Moves across the disc from the posterior to the anteror
Has very few photoreceptors

Question 31

Which is the first cell to be recruited in the ommatidia?

Answer 31

R8 - they are born with in the morphogenetic furrow

Question 32

How are R8 cells recruited?

Answer 32

Using a process of lateral inhibition through Notch singalling - this inhibits other cells to become R8 cells

Question 33

Describe the order which Rhabdomeres are recruited

Answer 33

1) R8, R2 and R5 secrete EGF pathway ligand Spitz
2) R3, R4 , then R1 and R6 recruited
3) R7 is the last
4) Then cone cells are recruited after

Question 34

Mutants lacking R7 can not see what?

Answer 34

UV light

This means they go towards white light rather than UV light

Question 35

Where are R8 cells born?

Answer 35

The morphogenic burrow

Question 36

Mutations in which genes causes the loss of R7?

Answer 36

Boss and sevenless

Question 37

What does the gene sevenless do?

Answer 37

Trans membrane receptor kinase
Activator of the Ras/Raf/Erk pathway
Expressed in R8,1,6,4,3,7 and con cells

Question 38

What does Boss do?

Answer 38

A membrane tethered ligand specific to sev

Expressed eclusively in R8