Signalling

Question 1

What is long range signalling known as and how does it work?

Answer 1

endocrine signalling
release of hormones into the bloodstream in animals and through the vascular system in plants

Question 2

Give an example of an endocrine signal in plants and its function.

Answer 2

the TF ‘CO’ accumulates in sunlight
when levels are high it promotes synthesis of FT signal protein which moves through sap from leaf to shoot which promotes flowering

Question 3

What is a cell that can respond to a certain signal said to be?

Answer 3

competent

Question 4

What is paracrine signalling?

Answer 4

intermediate range signalling

Question 5

What is juxtacrine signalling?

Answer 5

contact dependent (cell-cell) signalling

Question 6

During nerve system development, how do axons find and connect to other nerve cells?

Answer 6

by use of a growth cone at the end of the axon
guided by guidance molecules secreted along its route
grow towards attractive cues and grow away from repulsive cues

Question 7

What are the basic steps to a nerve signal?

Answer 7

1. electrical signal propagates from cell body of ‘presynaptic cell’ along its axon
2. the two cells contact each other at the synapse where the axon of one cell touches the cell body of another
3. electrical signal propagates along ‘post synaptic cell’

Question 8

What is the SRY?

Answer 8

Sex determining Region Y chromosome
a TF on the Y chromosome
regulates gene expression leading to testes differentiation

Question 9

How does the SRY signal promote development of male sex organs?

Answer 9

during development the embryo has both male and female structures
SRY signal causes the gonads to become testes (not ovaries)
allows male structures (Wolffian duct) to persist and the female structure (Mullerin duct) to dissapear

Question 10

What is meant by the ‘default’ in regards to cell signalling and give and example?

Answer 10

this is what happens unless a signal instructs an alternative fate
eg development of female sex organs, happens unless SRY signal is recieved

Question 11

Sexual dimorphism in birds is similar to humans in what ways?

Answer 11

have unequally sized sex chromosomes, male (ZZ) and female (ZW)
male and female embryos are initially indifferent

Question 12

What is the definition of a mosaic?

Answer 12

genetic change in cell lineage derived from a single zygote

Question 13

what is the definition of a chimera?

Answer 13

fusion of genetically distinct embryos

Question 14

What is a gynandromorph?

Answer 14

an organism with both male and female features

Question 15

What is meant by cell autonomous sex determination?

Answer 15

cells have intrinsic sex identity eg in chickens
longe range signalling is not primary component driving sexual dimorphism

Question 16

What is the sex determination mechanism in alligators?

Answer 16

temperature
known as temperature dependent sex determination (TSD)

Question 17

What do the different mechanisms of sex determination indicate?

Answer 17

signalling evolved to produce two sexes
two sexes didn’t produce signalling

Question 18

What is meant by the proximo-distal axis?

Answer 18

proximal ————————————-> distal
close to body distant from body

Question 19

What is meant by the proximo-distal axis?

Answer 19

along body axis
eg head anterior, feet posterior
eg thumb anterior little finger posterior

Question 20

What is the AER?

Answer 20

Apical Ectodermal RIdge
found at the tip of growing limb bud
promotes limb growth along proximo-distal axis by way of secreting signal proteins

Question 21

What is the signalling protein secreted by the AER?

Answer 21

FGF4, belonging to a family of secreted growth factors
FGF4 soaked beads can substitute the AER in limb growth

Question 22

What is a morphogen?

Answer 22

a substance active in pattern formation whose spatial concentration varies and to which cells respond differently at different concentrations

Question 23

What model explains development of digits along the anterior-posterior axis?

Answer 23

french flag model

Question 24

What is the ZPA?

Answer 24

Zone of Polarising Activity, found on the chick limb that produces a morphogen whose concentration along developing limb determines digit formation

Question 25

What protein is secreted by the ZPA?

Answer 25

sonic hedgehog (Shh)

Question 26

What is an organiser?

Answer 26

a signalling center that directs the development of the whole embryo or part of the embryo
eg ZPA

Question 27

How do trichomes ensure even spacing?

Answer 27

release signalling protein triptychon which inhibits neighbouring cells from becoming trichomes
v similar mechanism in drosophila hairs with the Notch signalling pathway, even though no similarity between notch and triptychon sequences

Question 28

How does juxtacrine signalling aid the formation of crypts in the gut?

Answer 28

EphB+ and EphrinB+ repel each other when in contact
during crypt development EphB+ cells are flanked either side by EphrinB+ cells so to escape have to move downwards thus creating a crypt

Question 29

What is autocrine signalling?

Answer 29

a cell responding to its own signals

Question 30

What two types of signalling are used in nerve growth cones.

Answer 30

Paracrine (Slit/Robo and Netrin/DCC)
Juxtacrine (Eph/Ephrin and Semaphorin/Plexin)

Question 31

Which side if the axis is the ZPA located?

Answer 31

The posterior side

Question 32

What is the name of the process by which drosophila hairs and plant trichomes are spaced?

Answer 32

Lateral inhibition