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History of Developmental Biology + the Germ Layers

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Ash Shehri

on 13 October 2014

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Transcript of History of Developmental Biology + the Germ Layers

1600s
1800s
1985
1990
1925
History of Developmental Biology
Pre-scientific Period
Early Scientific Period
Increased interest in the anatomy of the fetus as well as other structures
Based knowledge on classical concepts by Aristotle and Galen, rather than obsevation
Scientific Revolution of the 17 Century
Broke away from the classical observations (Harvey)
Discovery of optical instruments = means to learn more.
Recapitulation Period
New philosophy: romanticism
Focus on studying nature and its
changeability
out with the old, in with the new ideas
Developmental Mechanics
Scientists oppose Haeckel's recapitulation theory.
e.g. His: embryogenesis is the product of mechanical forces.
more experimentation led to more discoveries
Biochemistry and Cell biology
More questions arise as to how differentiation and specification occurs. Organizer considered to be hormonal.
New methods of examination e.g. electron microscope
Focus on cells rather than the embryo
importance of nucleus as the holder of genetic information; cloning
now called 'developmental biology'.
Molecular Biology and Genetic Engineering
molecular biology offered scientific techniques that were used in embryology.
developmental biology and evolution
medical applications in embryology
Future
:
genetic engineering through further merging of biology and molecular techniques.
Stem cell research

access to study embryos or gain knowledge
Egyptians and Babylonians were interested in congenital defects
Hippocrates
studied chicken embryos
Aristotle
classified animals according to whether they lay eggs, spontaneous generation, and viviparity
Galen
Greeks were highly interested in this matter
Leonardo da Vinci
Vesalius
Malpighi
Descartes' mechanical philosophy
Microscopists claim to see
homunculi
in eggs or sperm
Speculations about the age of the Earth
Preformation Theory
microscopy of chick embryos
claimed to have seen a
fully formed
embryo in an unincubated egg
Epigenesis
the structures of the adult form
arise
progressively
during development
everything in the embryos is
preformed

and simply gets bigger during development
Theory ran ahead of data
Cell Theory
All living organisms consist of cells
Cells come from cells
The egg is a single cell
Epigenesis won
Matthias Schleiden
Theodor Schwann
Preformation
EPIGENESIS
Recapitulation
Ideas on evolution arising
"ontogeny recapitulates phylogeny" - Ernst Haeckel
The distinction between germ cells and somatic cells.


August Weismann
Mosaicism - aspects of the final pattern are already arranged
in the embryo. If part of the embryo is destroyed a
corresponding part of the adult is lost.
Supported by Conklin’s study of ascidian embryos

Styela
1905

pigment in myoplasm
cells to become tail muscle
how cells become different
1880s
Determination - a stable change in the internal state of a cell
The state of determination of cells can be tested by
Transplantation.

Specification - cell will develop according to their fate even
when isolated.

Discovery of the Organizer by Spemann
preformation
germinal selection
epigenetic reactions between cells
Stem cells
The Germ Layers
Gastrulation is the process through which cells sort out to generate
the body plan
Gastrulation involves the inward movement of cell from the epiblast

Early embryonic
development

Topologies differ but a common theme -
Ectoderm precursors are segregated from early from
Progenitors that give rise to mesoderm and endoderm

The germ layers are established at gastrulation

Trophoblasts and Inner Cell Mass

Epiblasts and Hypoblasts

Early embryonic development
Full transcript