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What are the four major functions accomplished by development?

The generation of cellular diversity (differentiation)
The development of form (morphogenesis) within each generation
the promotion of growth of individuals
the continuity of life from one generation to the next through reproduction


What were the two dominant beliefs about how and organism might develop?

The mosaic model which proposed that the cells of an embryo had determinants which were unequally distributed in the cell and divided by asymmetric cell division controlling the fate of each cell
The regulative model that proposes that development is controlled by cellular signalling interactions


What evidence supported the mosaic model of development?

Wilhelm Roux supported Weismanns theory by destroying one cell of two cell frog embryo and noting that half a frog grew on the undamaged side suggesting that the fate of each cell was determined at each division


What evidence supported the regulative model of development?

Hans Driesch repeated the experiment of Wilhelm Roux, but instead of just destroying the cell he separated the two cells and found that one fully formed embryo developed
This suggested that in the earlier experiment the undamaged cell simply did not 'know' the other had been damaged and therefore did not try to account for it showing the importance of cellular interaction to the developmental process


What was the experiment performed by Hans Spemann and Hilde Mangold which showed the significance of inductive cell interactions?

Dorsal lip tissue from an early gastrula is transplanted into the region which usually becomes the ventral epidermis
The donor tissue invaginated to form a second embryonic axis leading to the formation of siamese twins
This showed the significance of cellular interaction in development


What are the 8 basic concepts of development?

Changes in cell behaviour underlie many aspects of development
Differential gene activity controls development
Development is progressive and the fate of cells becomes determined at different times
Cells differentiate in response to asymmetric cell division
Inductive interactions also make cells different
Patterning often involves the interpretation of positional information
Lateral inhibition can generate spacing patterns
the embryo contains a generative program


How can Changes in cell behaviour underlie many aspects of development?

Cells can change their behaviour through gene expression and therefore provide the link between the genetic program and the developmental progress
They do this through use of a limited behavioural repertoire:
Cell growth and division
Cell death/apoptosis
Cell adhesion
Cell Motility
Cell deformation
Cell communication
Cell differentiation
Cell memory


How does differential gene activity control development?

As almost all cells contain the same DNA the differences between the 210 cell types in the adult body must be due to the ability of the cell to turn genes on and off at the correct times


Why is development progressive?

At first embryos are divided up into broad regions such as germ layers but then these region continually become more and more broken down and the cells have there fates more and more finely determined


Why does asymmetric division cause cells to differentiate?

The daughter cells of these divisions will acquire different determinants and these will interact with different cellular activities causing different gene expression in different types of cells


How do inductive interactions make cells different?

Cells have receptors on them which will respond to signals given by the surrounding cells which can control its fate


What role does positional information play in patterning?

Positional information is obtained by the cell through morphogenetic gradients


What is patterning?

The control of what cells do across a tissue so that a form arrises


How does lateral inhibition generate spacing?

Developing structures may produce a short range inhibitor preventing the formation of similar structures nearby causing evenly spaced structures to form


Why is the genome of the embryo a generative program?

As each step will depend on what has just happened


What causes abnormal development?

The correct instructions are not in the egg
If there is genetic damage
If external factors influence the way cells behave