Development L3/4

Question 1

What are maternal effect mutations? (draw diagram)

Answer 1

Mutations have effect only when present in mother and none if present in father

Question 2

What did screening for maternal-effect mutations in drosophila reveal?

Answer 2

Genes encode products required for normal structure development a) along atero-prosterior axis b) in germ cell formation c) in dorso-ventral axis d) in embryo terminii

Question 3

How can antero-prosterior maternal effects be classed?

Answer 3

(see notes for diagram) –> bicoid, nanos, torso

Question 4

How can bicoid phenotype be rescued and how can you make head structures form in middle of embryo?

Answer 4

add WT anterior cytoplasm to bicoid mutant egg in diff places

Question 5

Draw bicoid maternal transcript and bicoid protein gradient

Answer 5

(see notes for diagram)

Question 6

How are bicoid and oskar made to segregate?

Answer 6

Transported along microtubules, specificity depends on 3’ UTR, bicoid moves with dynein to negative end (anterior), oskar moves with kinesin to positive end (prosterior)

Question 7

What happens if Oskar transcript fitted with bicoid 3’UTR?

Answer 7

Oskar mRNA move with bicoid RNA to anterior (-ve end) via dynein

Question 8

Why do cells move RNA and not protein itself?

Answer 8

1) Easier bc smaller 2) prevents protein function before it gets to the right place 3) can make a more localised higher conc –> all translated in one position allowing complexes that need high conc to form

Question 9

What is fucus and how does it put its axes in?

Answer 9

(see notes for diagram)

Question 10

How does Xenopus put its axes in?

Answer 10

(see notes for diagram)

Question 11

What does VegT code for and how does it and Wnt11 move?

Answer 11

VegT : codes for TF for growth factor, associates with yolk at vegetal pole
Wnt11: closer to the plasma membrane in the cortical cytoplasm, rotates by 30 degrees when sperm fertilises

Question 12

What do animal and vegetal parts of the embryo exclusively form if cultured separately?

Answer 12

Animal : ectodermal

Vegetal: endodermal

Question 13

When are mesodermal cell types formed?

Answer 13

When 2 halves of embryo come into contact

Question 14

What do vegetal cells do to help form mesoderm?

Answer 14

They are a source of signal telling animal cells to make mesoderm

Question 15

What is gastrulation?

Answer 15

When a 3d embryo forms from a 2d cell sheet, at the end the blastocoel (fluid-filled cavity in middle) is gone and embryo is surrounded by ectoderm, endoderm is internalised and mesoderm is between the 2
(epiboly = process of ectoderm moving round)

Question 16

What was the nobel-prize winning experiment designed to make embryos heterzygous for mutants that disrupt body patterning?

Answer 16

(see notes for diagram)

Question 17

What is used in drosophila to look at patterns?

Answer 17

The regular pattern of hooks (denticles)

Dentricles are the feet of larvae allowing them to grip and move through food source

Question 18

What are 3 main types of drosophila genes that dirupt early embryo patterning?

Answer 18

Gap gene, determines pair rule genes, determine segment polarity genes

Question 19

What is the hedgehog gene and why was it named this?

Answer 19

In mutant it produced dead embryo with prickly dentricle pattern
Encodes diffusible signalling molecule important for segment patterning, also found in vertebrates, termed sonic hedgehog(they already had 1 hedgehog gene :) )
Used for CNS and limb development

Question 20

What is the french flag model?

Answer 20

(see notes for diagram)
How positional values are interpreted depends on genetic instructions active in cell group and is influenced by their developmental history
Cells from one group transplanted to another read their new position and differentiate accordingly but following previously assigned program

Question 21

What is the proximo-distal sequence of chicken limb?

Answer 21

Humerus –> ulnar/radius –> wrist –> digits

Question 22

What is the antero-prostero sequence of digits?

Answer 22

2 –> 3 –> 4

Question 23

What happens when hind limb cells are transplanted into a fore limb bud?

Answer 23

They differentiate according to their position in the limb bud but make hind limb structures

Question 24

Draw diagram explaining progress zone

Answer 24

(see notes for diagram)

Question 25

How do cells in limb bud measure position in antero-prostero axis?

Answer 25

By reference to a prosterior part of the limb called the zone of polarising activity

Question 26

What generates the sonic hedgehog gradient in limb bud?

Answer 26

ZPA

Question 27

What happens if additional ZPA is grafted to anterior?

Answer 27

Cells differentiate to make mirror image duplication of prosterior digits (see notes for diagram)

Question 28

How can you avoid losing RNA when you fix cells?

Answer 28

Add an ms2 loop to RNA, then add protein with GPF which binds to ms2, makes RNA more stable, enabling you to look at RNA line (in situ hybridisation)

Question 29

What is the spemann organiser?

Answer 29

A clump of cells that provides all the signalling information necessary to trigger gastrulation

Question 30

Why does each drosophila single segment pattern as if it is its own unit?

Answer 30

Patterning entire embryo is hard but patterning single segment is easy