Early History And Basic Principles Of Development Flashcards
What are the two possibilities for animal development?
- Preformation theory
2. Epigenesis
Explain the preformation theory
Everything in the embryo is preformed at the beginning of development and gets bigger as it develops (one version- ‘homunculus’, little human embryo, in every sperm, at the head of the sperm believed the mother didn’t not give any genes)
Explain epigenesis
New structures arise by progressing through different stages (do not confuse with ‘epigenetic’)
Explain the the cell theory
. Organisms are composed of cells, the basic unit of life
. Both animals and plants are multicellular organisms that arise from a single cell, therefore development must be built upon (epigenesis) and not performed
. The fertilised egg is a single cell (the fertilised eggs), even though very specialised
. Microscopes allowed people to see cell and develop theories
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What processes are needed for development?
. Cell division (cleavage-nuclei divide and become enclosed)
. Pattern formation- spatial organisation of cells (organised in space- e.g. black or white stripes on a zebra)
. Morphogenesis- changes in form (relatively simple at the beginning and get more and mor complex)
. Differentiation- cell specialisation (starts unspecialised
. Growth
(These processes overlap and one can influence another)
Give 5 key cell activities
- Cell-cell communication
- Cell shape changes (during development)
- Cell movement (can start on the outside of the embryo, then a gap opens and it moves inside)
- Cell proliferation
- Cell death (apoptosis-some cells are born to die)
What is the A/P axis?
Anterior (head); posterior (tail)
What is the D/V axis?
Dorsal (upper or back); ventral (lower or front).
The mouth is always on the ventral side
What is the cranial?
Cephalic (refers to the head (anterior)
What is the rostral?
Towards the oral or nasal region
What is the Caudal?
Refers to tail or tail-like (posterior)
What is the P/D?
Proximal (bear), distal (far) from a given point. Often used for where an appendage joins the body (proximal) and the part furthest away (distal)
What is the medial?
Near the midline or middle
What is the lateral?
To the side
What is the apical?
At the apex, point or top
What is the basal?
At the base
What is a transverse (coronal) section?
Cross section
What is a Sagittarius (longitudinal) section?
Lengthways section
What is ‘pattern formation)?
Cells become organised in time and space and acquire an identity about what they will become - ‘positional information’
The early stages involve cells being allocated to different ‘germ layers’ that will give rise to different types of tissue
What does mosaic development depend on?
Specific ‘determinants’ in the zygote that are distributed unequally to the daughter cells during cleavage (only in some and not in others). The fate of each cell (what type is becomes) is predetermined in the egg by the factors it receives during cleavage. The cells environment cannot influence it. This relies on transfer of internal signals- depend on internal inheritance-not sensitive to the environment
What does regularise development depend on?
Regulative development depends on interactions between ‘pets’ of the developing embryo by cell to cell communication. The cells environment (the other cells surrounding it) can influence it’s developmental fate. The embryo is able to develop normally even when parts of it are removed or rearranged. So if you mix the cells up the same product will be formed
What are germ cells present?
The cytoplasm
What was the experiment carried out by Wilhelmina Roux (1888) that provided the early evidence of mosaic development?
He destroyed one cell of a two-cell embryo with a hot needle (to kill the cell) to result in a half-embryo so, the cell couldn’t compensate for the loss of one of early cells. He concluded that frog development is mosaic, so that the cells have their character and fate determined at each stage
