Early History And Basic Principles Of Development

Question 1

What are the two possibilities for animal development?

Answer 1

1. Preformation theory

2. Epigenesis

Question 2

Explain the preformation theory

Answer 2

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)

Question 3

Explain epigenesis

Answer 3

New structures arise by progressing through different stages (do not confuse with ‘epigenetic’)

Question 4

Explain the the cell theory

Answer 4

. 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

Question 5

Middle page 53

Answer 5

…

Question 6

What processes are needed for development?

Answer 6

. 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)

Question 7

Give 5 key cell activities

Answer 7

1. Cell-cell communication
2. Cell shape changes (during development)
3. Cell movement (can start on the outside of the embryo, then a gap opens and it moves inside)
4. Cell proliferation
5. Cell death (apoptosis-some cells are born to die)

Question 8

What is the A/P axis?

Answer 8

Anterior (head); posterior (tail)

Question 9

What is the D/V axis?

Answer 9

Dorsal (upper or back); ventral (lower or front).

The mouth is always on the ventral side

Question 10

What is the cranial?

Answer 10

Cephalic (refers to the head (anterior)

Question 11

What is the rostral?

Answer 11

Towards the oral or nasal region

Question 12

What is the Caudal?

Answer 12

Refers to tail or tail-like (posterior)

Question 13

What is the P/D?

Answer 13

Proximal (bear), distal (far) from a given point. Often used for where an appendage joins the body (proximal) and the part furthest away (distal)

Question 14

What is the medial?

Answer 14

Near the midline or middle

Question 15

What is the lateral?

Answer 15

To the side

Question 16

What is the apical?

Answer 16

At the apex, point or top

Question 17

What is the basal?

Answer 17

At the base

Question 18

What is a transverse (coronal) section?

Answer 18

Cross section

Question 19

What is a Sagittarius (longitudinal) section?

Answer 19

Lengthways section

Question 20

What is ‘pattern formation)?

Answer 20

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

Question 21

What does mosaic development depend on?

Answer 21

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

Question 22

What does regularise development depend on?

Answer 22

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

Question 23

What are germ cells present?

Answer 23

The cytoplasm

Question 24

What was the experiment carried out by Wilhelmina Roux (1888) that provided the early evidence of mosaic development?

Answer 24

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

Question 25

Sea urchin embryos show regulative development how?

Answer 25

Regulative development depends on interactions between parts of the developing embryo and can result in causing different tissues to form (even if parts of the original embryo are removed or rearranged). Half the cell had been destroyed but it still developed the same so, the embryo compensated for one of the two cells it started out with supports environment control idea