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BMS242 Developmental Biology > L7 - Drosophila Body Plan > Flashcards

L7 - Drosophila Body Plan Flashcards

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1
Q

What organisms can segmentation be seen in?

A

Many even humans just is slighlty more obscure

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2
Q

How quickly is patterning established in drosophila

A

Very quciky - within 24 hours

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3
Q

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

A

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

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4
Q

What did Volhard and Wischauus perform in 1979/1980

A

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

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5
Q

How many lines did Volhard and Wischauus establish

A

26,978

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6
Q

How many complementation groups (genes) established

A

139

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7
Q

What are complementation tests needed for

A

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

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8
Q

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

A

1 - haplosufficent

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9
Q

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

A

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

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10
Q

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

A

Shows they are in different genes ==> complement

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11
Q

What is saturation mutagenesis

A

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

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12
Q

Desribe gap genes when mutated

A

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

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13
Q

What are gap genes required for

A

To specify large regions of the body

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14
Q

Example of a gap gene

A

Knirps

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15
Q

Describe the effect of a mutation in a par rule gene

A

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

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16
Q

Example of a paired rule gene (2)

A

Even/odd skipped

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17
Q

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

A

Loss of polarity of the segment

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

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18
Q

Hieracrchy for gene interaction during development

A

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

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19
Q

Describe the action of maternal genes

A

Progressively divide up the mebryo

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20
Q

Where is bicoid locaised

What is bicoid

How does it act

A

At the anterior

DNA binding transcriptional activator

Acts a morphogen

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21
Q

When are high afifnity bicoid binding sites activated

A

At lower threshold concentrations

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22
Q

When are low affinity bicoid binding sites activated

A

At higher thresholds concs

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23
Q

Where is nanos localised

A

At the posterior

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24
Q

Describe the pheno of a bicoid mutant egg

A

Lacks all of the anterior structures

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25
Q

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

A

Some anterior structures develop

Partial rescue of the phenotype

26
Q

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

A

Ectopic head in the middle

Mirror image of the thoracic segements going outwards

27
Q

Describe the effect on striping of low levels of bicoid

A

5 stripes instead of 7

28
Q

Describe the effect on striping of normal bicoid levels

A

7 stripes

29
Q

Describe the effect on striping of overexpressing bicoid

A

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

30
Q

Bicoid gradient converted to

A

Hunchback gradient

31
Q

Gap genes are a read out of

A

Bicoid gradient

32
Q

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

A

Activation and repression

33
Q

Where is Krupple expressed in the wild type

A

Discrete band in the middle of the embryo

34
Q

Where is Krupple expressed in a bicoid mutant

A

Expressed throughout the entire anterior domain of the embryo

35
Q

Pair rule expression is controlled …

A

Bit by bit

36
Q

Pair rule expression dependent on

A

The interaction of postively and negatively acting transcriptional regulators

37
Q

Describe the expression of engrailed

A

In the anterior of each parasegment

In the posterior of each segement

38
Q

What is the difference between segements and parasegements

A

They are 1/2 a segement out of phase

39
Q

Where are Hh and Wg expressed

A

In adjacent cells

40
Q

What is Hh expression dep. on

A

The expression of Wg

41
Q

What is Wg expression depend on

A

The expression of Hh

42
Q

Hh and Wg are …

A

MUTUALLY DEPENDENT PATHWAYS

43
Q

What does Wg expression repress

How is this seen in a mutant phenotype

A

Supresses formation of the denticles

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

44
Q

Wg morphogen gradient is

A

Asyymetric

45
Q

What do Hox genes provide

A

Positional information to each of the segments

46
Q

Expression of Hox genes is in the same order as

A

Genes are laid out in the genome

47
Q

What do HOX genes code for

A

DNA binding TFs

48
Q

What is the same about each HOX gene

A

Binds to the same region of DNA but has different effects

49
Q

What are the two hox clusters in drosophila

A

Antennapedia complex

Bithorax complex

50
Q

What 3 hox genes are in the bithroax complex

A

UBX ABD-A ABD-B

51
Q

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

A

Long Since all of the segments are formed at once

52
Q

Describe development in short and intermeidate germ band insects

A

Start with the head and thoracic segments

Abdominal segments are then added sequentially

53
Q

Describe the segment addition in Strigamia martima

A

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

54
Q

What is involved with the notch pathway

A

Her/Hes4

55
Q

Describe the cycling of the notch pathway

A

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

56
Q

Why is there a time delay in the notch clock

A

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

57
Q

What does notch activation cause

A

Downregulation of the delta ligand

58
Q

What does the Notch-delta time delay cause

A

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

59
Q

THe common ancestor of vert and invert likely used …

A

The notch clock as a method for segmentation

60
Q

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

A

Presomatic mesoderm - fish

Primitive streak - chick

61
Q

Where to the majority of the known candidate pacemaker genes lie

A

In the notch pathway

BMS242 Developmental Biology (17 decks)

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