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History of Developmental Biology + the Germ Layers
Transcript of History of Developmental Biology + the Germ Layers
History of Developmental Biology
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.
New philosophy: romanticism
Focus on studying nature and its
out with the old, in with the new ideas
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
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
studied chicken embryos
classified animals according to whether they lay eggs, spontaneous generation, and viviparity
Greeks were highly interested in this matter
Leonardo da Vinci
Descartes' mechanical philosophy
Microscopists claim to see
in eggs or sperm
Speculations about the age of the Earth
microscopy of chick embryos
claimed to have seen a
embryo in an unincubated egg
the structures of the adult form
everything in the embryos is
and simply gets bigger during development
Theory ran ahead of data
All living organisms consist of cells
Cells come from cells
The egg is a single cell
Ideas on evolution arising
"ontogeny recapitulates phylogeny" - Ernst Haeckel
The distinction between germ cells and somatic cells.
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
pigment in myoplasm
cells to become tail muscle
how cells become different
Determination - a stable change in the internal state of a cell
The state of determination of cells can be tested by
Specification - cell will develop according to their fate even
Discovery of the Organizer by Spemann
epigenetic reactions between 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
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