L7 - Drosophila Body Plan

Question 1

What organisms can segmentation be seen in?

Answer 1

Many even humans just is slighlty more obscure

Question 2

How quickly is patterning established in drosophila

Answer 2

Very quciky - within 24 hours

Question 3

Describe what can be seen of a scanning EM of the early drosophila embryo

Answer 3

Can see the first folds are the basis for the first segments

Question 4

What did Volhard and Wischauus perform in 1979/1980

Answer 4

Undertook a saturation mutagenesis to identify genes involved in the development and patterning of the naked cuticle

Question 5

How many lines did Volhard and Wischauus establish

Answer 5

26,978

Question 6

How many complementation groups (genes) established

Answer 6

139

Question 7

What are complementation tests needed for

Answer 7

To test whether different genes had been hit or if it was the same gene which had been hit many times

Question 8

How many copies of the gene are required usually for normal function

Answer 8

1 - haplosufficent

Question 9

Describe the results for A/B where a phenotype was produced

Answer 9

Shows that they are the same gene ==> fail to complement

Question 10

Describe the results for A/C where no phenotypes are produced

Answer 10

Shows they are in different genes ==> complement

Question 11

What is saturation mutagenesis

Answer 11

Hitting the genes many times on average - so can be statisitcally confident that there are no more genes - as these would have also have been hit

Question 12

Desribe gap genes when mutated

Answer 12

Leads to gaps (e.g. loss of the middle section of the abdomen)

Question 13

What are gap genes required for

Answer 13

To specify large regions of the body

Question 14

Example of a gap gene

Answer 14

Knirps

Question 15

Describe the effect of a mutation in a par rule gene

Answer 15

Pairs are missing - e.g. every other segement is missing

Question 16

Example of a paired rule gene (2)

Answer 16

Even/odd skipped

Question 17

What is the effect of a mutation in a segment polarity gene

Answer 17

Loss of polarity of the segment

EG –> loss of the naked cuticle part of the sgement

Question 18

Hieracrchy for gene interaction during development

Answer 18

Maternal genes –> Gap genes –> Pair rule genes –> Segment polairity genes

Question 19

Describe the action of maternal genes

Answer 19

Progressively divide up the mebryo

Question 20

Where is bicoid locaised

What is bicoid

How does it act

Answer 20

At the anterior

DNA binding transcriptional activator

Acts a morphogen

Question 21

When are high afifnity bicoid binding sites activated

Answer 21

At lower threshold concentrations

Question 22

When are low affinity bicoid binding sites activated

Answer 22

At higher thresholds concs

Question 23

Where is nanos localised

Answer 23

At the posterior

Question 24

Describe the pheno of a bicoid mutant egg

Answer 24

Lacks all of the anterior structures

Question 25

Describe the pheno of a bicoid mutant egg which has had some anterior wt egg cytoplasm transplanted into the anterior

Answer 25

Some anterior structures develop Partial rescue of the phenotype

Question 26

Describe the pheno of a bicoid mutant egg which has had some anterior wt egg cytoplasm transplanted into the MIDDLE

Answer 26

Ectopic head in the middle | Mirror image of the thoracic segements going outwards

Question 27

Describe the effect on striping of low levels of bicoid

Answer 27

5 stripes instead of 7

Question 28

Describe the effect on striping of normal bicoid levels

Answer 28

7 stripes

Question 29

Describe the effect on striping of overexpressing bicoid

Answer 29

Stripes still form but pushed much more anteriorly = large gap between anterior tip and first pair rule gene BECAUSE bicoid is now too high at the extreme anterior to allow the development of the head structures

Question 30

Bicoid gradient converted to

Answer 30

Hunchback gradient

Question 31

Gap genes are a read out of

Answer 31

Bicoid gradient

Question 32

Different gap genes are activated at different th concs, this is a balance between

Answer 32

Activation and repression

Question 33

Where is Krupple expressed in the wild type

Answer 33

Discrete band in the middle of the embryo

Question 34

Where is Krupple expressed in a bicoid mutant

Answer 34

Expressed throughout the entire anterior domain of the embryo

Question 35

Pair rule expression is controlled ...

Answer 35

Bit by bit

Question 36

Pair rule expression dependent on

Answer 36

The interaction of postively and negatively acting transcriptional regulators

Question 37

Describe the expression of engrailed

Answer 37

In the anterior of each parasegment | In the posterior of each segement

Question 38

What is the difference between segements and parasegements

Answer 38

They are 1/2 a segement out of phase

Question 39

Where are Hh and Wg expressed

Answer 39

In adjacent cells

Question 40

What is Hh expression dep. on

Answer 40

The expression of Wg

Question 41

What is Wg expression depend on

Answer 41

The expression of Hh

Question 42

Hh and Wg are ...

Answer 42

MUTUALLY DEPENDENT PATHWAYS

Question 43

What does Wg expression repress How is this seen in a mutant phenotype

Answer 43

Supresses formation of the denticles Wg (-/-) - hedgehog phenotype - lawn of denticles as there is no supression of hair development

Question 44

Wg morphogen gradient is

Answer 44

Asyymetric

Question 45

What do Hox genes provide

Answer 45

Positional information to each of the segments

Question 46

Expression of Hox genes is in the same order as

Answer 46

Genes are laid out in the genome

Question 47

What do HOX genes code for

Answer 47

DNA binding TFs

Question 48

What is the same about each HOX gene

Answer 48

Binds to the same region of DNA but has different effects

Question 49

What are the two hox clusters in drosophila

Answer 49

Antennapedia complex | Bithorax complex

Question 50

What 3 hox genes are in the bithroax complex

Answer 50

UBX ABD-A ABD-B

Question 51

Is drosophila a long or short germ band insect - why?

Answer 51

Long Since all of the segments are formed at once

Question 52

Describe development in short and intermeidate germ band insects

Answer 52

Start with the head and thoracic segments | Abdominal segments are then added sequentially

Question 53

Describe the segment addition in Strigamia martima

Answer 53

When a number of genes cloned and an in-situ performed notch and delta were easily defined

Question 54

What is involved with the notch pathway

Answer 54

Her/Hes4

Question 55

Describe the cycling of the notch pathway

Answer 55

When notch activated in the cell the levels of delta become downreg When one cell is active the adjacent one becomes down regualted

Question 56

Why is there a time delay in the notch clock

Answer 56

Time delay to allow for the changes in gene transcription and translation

Question 57

What does notch activation cause

Answer 57

Downregulation of the delta ligand

Question 58

What does the Notch-delta time delay cause

Answer 58

An oscillation between strong and weak signalling levels - propagation of this signals between cells then causes a wave of activation

Question 59

THe common ancestor of vert and invert likely used ...

Answer 59

The notch clock as a method for segmentation

Question 60

____________ (in fish) and ___________ (in chick) cycle to give rise to the somites

Answer 60

Presomatic mesoderm - fish | Primitive streak - chick

Question 61

Where to the majority of the known candidate pacemaker genes lie

Answer 61

In the notch pathway