Evolutionary Biology 4: Principles of Development

Question 1

Hierachal organisation of tissue development

Answer 1

Stem cells
- Undifferentiated, self-renewing cell can give rise to differentiated and undifferentiated cells alike

Progenitor cells
- Undifferentiated, dividing cell whose potential is restricted to one or few fates with limited self-renewing potential

Precursor cells
- Undifferentiated, dividing cell giving rise to a specific cell type

Question 2

Specification -> Determination -> Differentiation

Explain states of cell development

Answer 2

Specification = Labile state where fate is acquired but can still be altered

Determination = Stable state where fate is acquired and can no longer be altered

Differentiation = process by which developing cells acquire a unique identity (final)

Question 3

During fate restriction, cells undergo …..?…. with regards to genetics

Answer 3

Changes in gene expression

Question 4

Characteristics of autonomous specification

Answer 4

Autonomous specification

• cell fate independent of interactions with neighbouring cells
• governed by ‘cytoplasmic determinants’ (mRNAs and proteins unequally distributed in egg cytoplasm)
• these are asymmetrically approportioned to cells during division (daughter cells)
• determined by cell lineage, exclusively internal factors

Question 5

Characteristics of conditional specification

Answer 5

Conditional specification

• cell fate determined by interactions with neighbouring cells
• positional information
• fate can be altered by changing the surrounding environment (and therefore signals)
• common to vertebrates and plants

Question 6

Characteristics of syncytial specification

Answer 6

Syncytial Specification

• in insect centrolecithal cleavage (and the endosperm of angiosperm) cell fate can be determined by factors in syncytium
• Nuclei contained in common cytoplasm (syncytium)
• Fate is determined by gradients of determinants in syncytium

Question 7

What is a morphogen? Explain the effect of different concentrations

Answer 7

A chemical that acts in a concentration-dependent manner to instruct the development of tissues

Different concentrations will cause activation of different sets of genes

Question 8

2 Examples of morphogens (1 animal, 1 plant)

Answer 8

Animal - sonic hedgehog

Plant - Auxin