Fundamentals of Genetics, Evolution, and Development 18: Development: Embryology

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Fundamentals of Genetics, Evolution, and
Development18 Development Embryology

• Bio 1111
• Christopher T. Cole
• University of Minnesota, Morris

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18 Development Embryology

• Reading Moore
• Ch. 19 The Century of Discovery
• Ch. 20 Descriptive Embryology (to p. 433)
• Ch. 22 Interactions during Development (pp.
  476-486)
• Recommended Life
• 7th ed Ch. 20 Animal Development
• 8th ed Ch. 43 Animal Development

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outline

• descriptive
• morphogenesis Haeckel von Baer
• early embryogenesis
• blastula, gastrula, neurula, pharyngula
• experimental
• Spemann, Mangold

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main points

• comparative embryology embryos of very different
  vertebrates look very simlar more similar at
  earlier stages progressive differentiation
• What does comparative embryology tell us about
• evolution?
• development?
• genetics?

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Embryology Questions

• How is the development from a single cell to a
  complex, differentiated, multicellular organism
  controlled?
• Are the directions distributed throughout the
  developing organism? Or does one part direct the
  development of the whole?

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Embryology Questions

• How are evolution and embryology related?
• Both appear to display a progressive unfolding of
  potential form function

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Embryology Questions

• How can study of these related questions be
  made scientific? i.e. how can ideas be made
  testable?
• Especially ca. 100 years ago, ideas about this
  were very fuzzy, even as experimental evidence
  began to accumulate
• Synthesis with modern evolutionary genetic
  theory came much later than other fields of
  biology now a very active area of research

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Darwin on Embryology

• Letter to Asa Gray
• Embryology provides the most important evidence
  regarding evolution not just the fact that it
  has happened, but how it has happened

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In Origin (how not to write)

• Thus, as it seems to me, the leading facts in
  embryology, which are second in importance to
  none in natural history, are explained on the
  principle of slight modifications not appearing,
  in the many descendents from some one ancient
  progenitor, at a very early period in the life of
  each, though perhaps caused at the earliest, and
  being inherited at a corresponding not early
  period.

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I have seldom seen a more pleasant, cordial
frank man C. Darwin
Of all the young men Darwin met, this was the
one who most behaved like a religious
disciple. Haeckel became by far the most
ardent Darwinian in Germany, influencing a
generation of scholars that included Anton
Dohrn, Hans Driesch, Hans Spemann, and Richard
Goldschmidt. Janet Browne
Ernst Haeckel
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Haeckels interpretation
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Haeckels Biogenetic Law

• Ontogeny recapitulates phylogeny
• Development of an individual repeats the
  evolutionary history of a species
• Evolution proceeds by adding modifications onto
  pre-existing states
• Not!

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Haeckels Biogenetic Law

• Haeckel conceived of evolution like a ladder
  start with slime, end up with humans
• Sought to unify ideas of Goethe, Lamarck, and
  Darwin
• Also coined the term ecology

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A disastrous union of embryology and
evolutionary biology was forged in the last half
of the nineteenth century by the German
embryologist and philosopher Ernst
Haeckel --Scott F. Gilbert
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• von Baer discovered
• - blastula
• notochord
• germ layers of embryos
• mammalian development
• from eggs

Karl Ernst von Baer 1792-1876 (preceded Haeckel)
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von Baers Laws

• The general characters of the group an embryo
  belongs to appear earlier in development than the
  special characters
• Structural relations are formed with increasing
  specialization
• The embryo of a species does not pass through
  other definite forms, but progressively differs
  from them

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von Baers Laws

• Fundamentally, the embryo of a higher animal form
  never resembles the adult of another animal form,
  but only its embryo
• von Baers conception of evolution was like a
  bush a branching phylogeny

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von Baers interpretation
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At what stage do we find species-specific characte
rs? What characters are shared by many
taxa, e.g. the whole vertebrate class?
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egg 1 cell

blastula hollow single layer
gastrula 3 layers
pharyngula differentiated along axis
neurula tubular structures
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Development of a frog tadpole
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Amphioxus (lancet), a primitive chordate
What defines a chordate (phylum Chordata)?
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5 characters defining Chordates
dorsal, tubular nerve cord (DTNC)
notochord
ventral heart tail
pharyngeal gill slits
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dorsal, tubular nerve cord ventral heart
dorsal heart ventral nerve cord(s)
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What kinds of organisms are these?
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Human embryo development fifth week
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What happens at the earliest steps?
Fertilization
Purves et al. 2003 Life
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Pattern of cell division depends on the amount
of yolk
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Fate Map of a frog blastula
Skin, nervous system
Gut lining, liver lungs
muscle, bone, kidneys, blood gonads, connective
tissues
Inject stain into a few cells and see where they
end up in later larval stage
Purves et al. 2003 Life
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Figure 20.8 Gastrulation in Sea Urchins
blastocoel
primary mesenchyme
Gastrulation in a sea urchin embryo
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Gastrulation in an amphibian embryo
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Primary germ layers
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Movie Gastrulation

• Purves et al. Life
• CD video clips 20.3, 20.5

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What happens in a really BIG egg? Macrolecithal
egg of chickens embryo divides, yolk does not
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Figure 20.15 Neurulation in the Frog Embryo
(Part 2)
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Figure 20.16 The Development of Body
Segmentation
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From descriptive to experimental embryology
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Hans Spemann
Hilde Mangold
Max Plank Institute
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Figure 20.10 Spemanns Experiment
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Induction one structure induces specific
development of another
note totally different meaning of induction
from previous use!!
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Induction in eye development
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Induction in limb development wing bud in
chicken
inner layer induces outgrowth of outer layer
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Differentiaton requires establishing more
information about postion in embryo
distal vs. proximal
anterior vs. posterior
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Ablation and transplant experiments demonstrate
induction
Transplant AER
Transplant ZPA
Normal
Ablation
Apical Ectodermal Ridge
Zone of Polarizing Activity