Developmental biology is the study of the processes by which organisms grow and develop. It expanded on classical embryology by using modern molecular techniques and genetic approaches. Some key areas of study include differentiation, morphogenesis, growth, reproduction, evolution, and environmental influences. Early debates centered around whether embryonic structures were preformed in the egg (preformationism) or arose de novo through epigenesis. Landmark studies in the 1800s by scientists like Pander, von Baer, and Rathke established germ layer formation and embryonic development principles. Lineage tracing techniques using dyes were later developed to track cell lineages in living embryos of organisms like tunicates, amphibians, zebrafish, and frogs.
2. Developmental Biology vs
Embryology
Embryology
– observational biology
– experimental manipulations
Developmental Biol
– expands embryological studies using molecular
techniques
– used genetic approaches to study model
systems
3. Developmental Biology
Approaches in Other Fields
Cancer Biology
Neuroscience
The answers to questions in these fields
require knowing when during development
particular events occur
4. Developmental Biology is
Defined by the Questions Asked
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental
Integration
5. 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
6. 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
7. 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
8. 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
9. 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
10. 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
11. 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”
12. 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
13. 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
14. 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
15. 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
16. 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
18. 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