Lecture 11 Flashcards
What is the preformation theory?
Everything in the embryo is preformed and gets bigger as it develops
What is the Epigenesis theory?
New structures arise by progressing through different stages
Schleiden and Schwann (1938)
Organisms are composed of cells, the basic unit of life. Both animals and plants are multicellular organisms that arise from a single cell so must be EPIGENESIS theory.
August Weismann (1834-1914) THE GERM LINE CONCEPT
Only germ cells pass on characteristics to the offspring. The body is just a carrier of germ cells.
What processed are needed for development?
.Cell division .Pattern formation .Morphogenesis .Differentiation .Growth
What is pattern formation?
Cells become organised in time and space and acquire an identity about what they will become. Early stages involve cells being allocated to different germ layers that will give rise to different types of tissue.
Who do the different germ layers give rise too?
Endoderm- gut, liver, lungs
Mesoderm- skeleton, muscle, kidney, heart, blood
Ectoderm- skin and nervous system.
What is mosaic development?
Development depends on specific determinants in the zygote that are distributed unequally to daughter cells during cleavage.
The fate of each cell is PREDETERMINED in the egg by factors during cleavage and environment cannot influence it.
What is regulative development?
Development depends on interaction between parts of the developing embryo by cell to cell communication. The cells environment can influence its development fate.
Wilhelm Roux (1888)
destroyed a cell of a two-cell embryo to result in a half embryo. Concluded frog development is mosaic.
Hans (1891)
Regulative development depends on interactions between parts of the developing embryo and can result in causing different tissues to form.
Is development mosaic or regulative?
BOTH
-Haha tricked you lol
