developmental biology introduction. developmental biology vs embryology 4 embryology...
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Developmental Biology
Introduction
Developmental Biology vs Embryology Embryology
– observational biology– experimental manipulations
Developmental Biol– expands embryological studies using molecular techniques– used genetic approaches to study model systems
Developmental Biology Approaches in Other Fields Cancer Biology Neuroscience
The answers to questions in these fields require knowing when during development particular events occur
Developmental Biology is Defined by the Questions Asked Differentiation Morphogenesis Growth Reproduction Evolution Environmental Integration
What goes on as an embryo develops from a single, pluripotent cell into a complete organism?
Majority of dev systems are multicellular
Single-celled systems used to study cellular differentiation
Differentiation Morphogenesis Growth Reproduction Evolution Environmental Integration
Developmental Biology is Defined by the Questions Asked
Cell movements & tissue reorganizations
How do differentiated cells move and reorganize during development to generate functional organisms?
Major point of study for classical embryology
Developmental Biology is Defined by the Questions Asked Differentiation
Morphogenesis Growth Reproduction Evolution Environmental Integration
What are the limiting factors for cell division
Allometric growth - varying rates of mitosis in regions of the embryo
Isometric growth- equal rates of mitosis throughout embryo
Developmental Biology is Defined by the Questions Asked Differentiation Morphogenesis
Growth Reproduction Evolution Environmental Integration
The germ plasm
Gametogenesis - formation and maintenance of pluripotent, haploid germ cells (gametes)
Recognition & interaction of gametes at fertilization
Developmental Biology is Defined by the Questions Asked Differentiation Morphogenesis Growth
Reproduction Evolution Environmental Integration
Survivability of evolutionary mutations is limited by restraints of embryogenesis
Evolutionary changes must be small changes for the embryo
What are the evolutionary relationships between groups of organisms
Developmental Biology is Defined by the Questions Asked Differentiation Morphogenesis Growth Reproduction
Evolution Environmental Integration
Early development of many organisms is influenced by environmental cues
Examples: color/shape of butterfly larvae (caterpillars)diapause in invertebrates in vernal pools
Developmental Biology is Defined by the Questions Asked Differentiation Morphogenesis Growth Reproduction Evolution
Environmental Integration
Aristotle (300BC)– credited with 1st notions on embryology
William Harvey (mid 1600s)– hypothesized that all animals originate from an egg
Marconi Malpighi (late 1600s)– drew 1st micrographs of developing chick embryos
– ignited debate between preformationist and epigenesists
Early “Embryologists”
Preformation– Embryonic structures are preformed within the
gamete (either egg or sperm)
Epigenesis– the embryonic structures arise anew from the
interaction of substances within the gametes
Preformation vs Epigenesis
Malpighi found embryonic structures in “unincubated” eggs– these eggs were left in the warm sun of
southern Italy during the summer months– So although they were unincubated, they were
not unfertilized and some embryonic development occurred
Malpighi’s observation spurned the preformationist
Preformation vs Epigenesis
Preformationist vs Epigenesis
Unusual Hypotheses of Preformationists– a tiny preformed being present in the gamete
• This being would also have even tinier beings within it’s embryonic germ cells
– and those tinier beings would have tinier still beings within their gametes
» and so on and so on» and so on and so on» and so on and so on» and so on and so on» and so on and so on
Pervasiveness of preformationist ideas– Fertilization had never been observed– There was as yet (1600s) no cell theory to give
a lower limit to the size a cell could have
Preformation vs Epigenesis
Christian Pander– visualized epigenesis of embryonic germ layers
Karl Ernst von Baer– described notochord, discovered mammalian
egg, proposed 4 laws of development
Heinrich Rathke– described pharyngeal arches, skull formation
The First Embryologists ca1820
First Embryologists
Germ Layers (Pander)
1. general characters of a [genus] appear earlier during development than characters of [species]
2. more specific characters derive from more general characters
3. the embryo of a given species diverges form the adult form of lower animals rather than passing through the adult forms of lower animals
4. early embryos of higher animals never looks like a lower animal, but does resemble the embryo of lower animals
Ernst von Baer’s Laws
First Embryologists
Rathke’s Skull Studies
Lineage Tracing
Observations of pigmented cells in living Tunicate embryos (E.G. Conklin, 1905)
Conklin’s Drawings of Tunicate Embryogenesis: Tracing Muscle Lineage
Lineage Tracing in Amphibian Embryos with Vital Dyes
Lineage Tracing in Zebrafish with Fluorescent Dyes
Lineage Tracing in Xenopus with Fluorescent Dyes