Principles of Animal Development

Question 1

Model organisms and humans share recognisable homology 

Answer 1

 ≈ 50% of protein-encoding genes in humans have recognisable homologues in Drosophila, C. elegans, and mice 

Protein families involved in cell interactions and cell signalling frequently shared 

Gene duplications in higher animals  more family members

Question 2

The developmental potential becomes restricted

Answer 2

Individual cells become more and more restricted in their development potential. This is accompanied by the acquisition of a specific gene expression pattern. Genes are switched on and off.

Question 3

Spatial patterning

Answer 3

Cells become different according to their positions in the embryo. This means they must respond to the stimuli produced by other cells.

• A group of cells might start with the same potential but then an extracellular signal induces one or more of the cells to change character. This is called Inductive Signalling.

Question 4

Combinational signalling and cell memory

Answer 4

A) Multiple signals concurring on one cell give rise to different cells 

B) Cell memory (cells retain a record of what they have been and signals their ancestors have received) and therefore will respond to a stimulus based on this memory.

Question 5

Concentration gradients of signalling molecules provide positional information

Answer 5

C) Different concentration of morphogen induce different gene expression patterns

Question 6

C) Different concentration of morphogen induce different gene expression patterns

Answer 6

Each cell can produce a substance x that acts on the other cell to inhibit the production of x. This is called lateral inhibition.

Question 7

Asymmetric divisions generate diversity

Answer 7

1. Asymmetric Division : Sister cells born different

2. Symmetric Division : Sister cells become different as a result of difference’s on influences

Question 8

Subsequent steps must be highly coordinated

Answer 8

The appropriate type of change 

In the right place

 Along body axis 

Dorsal/ventral 

Left/right 

At the right time 

Some molecular principles follow  Much more detail in Alberts, Ch 22 (on CD)

Question 9

Summary: introduction to early development

Answer 9

 Model organisms provide basic insights that extend to related organisms 

C. elegans – worms 

D. melanogaster – insects 

M. musculus – mammals

Both principles and molecular mechanisms are “re-used” across clades and at different stages of development