Chapter 8 - Principles of Development

Notes for Chapter 8:
Principles of Development

Click link to return to Lecture Schedule
or back to Chapter 7
or ahead to Chapter 11

Chapter 8 Assignment:

Ch. 8: 156-170; RQ8: 2-3,5-8,13-14

Here is link to Animated Urchin Fertilization and Development Processes demonstrated in lecture.

Introduction: The Primary Organizer

source of image
Featured Scientist: Hans Spemann

Links: 1 - 2 - 3 - 4 - 5 - 6

Can you answer this question about Spemann's experiment on Embryonic Induction?

Key Terms: primary organizer

Links to Selected Developmental Biology Websites: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9

I. Early Concepts: Preformation vs. Epigenesis (Skim)

Key Terms: preformation vs. epigenesis, deterministic development, cytoplasmic localization, induction

Preformation and Homunculus Concept
1. Argument based on premise thatsomething cannot come from nothing
2. Development was likened to Russian nesting dolls
3. Entire history of humankind was presumed to be contained within Adam’s sperm
4. Development was literally “unfolding”

Epigenesis prevailed in the end
1. ‘upon formation’ new structures arise progressively
2. Cell theory was especially influential
3. Egg is single, specialized cell
4. Characteristics are inherited from germ cells, not body (somatic) cells

II. Fertilization
Links to Gametogenesis and Fertilization Labs

Key Terms: fertilization, zygote, germinal vesicle, activation, fertilization cone, polyspermy, fertilization membrane

Fertilization (as represented by sea urchin eggs)
1. Interaction between sperm & egg is elaborate
2. Zygotes typically have mechanisms to avoid polyspermy
once Fertilization occurs
3. Fusion of sperm and egg restores diploidy

III. Cleavage and Early Development
Links to Early Development Labs

Key Terms: blastomeres, embryonic polarity

Key Events in Development
1. Gametogenesis
2. Fertilization
3. Cell cleavage
4. Gastrulation (forms gut)
5. Organogenesis
6. Growth

a) Patterns of cleavage

Key Terms: yolk content, isolecithal (with holoblastic cleavage) vs. meso- or telolecithal (with meroblastic cleavage), vegetal vs. animal pole, indirect development (embryo -> larva -> metamorphosis -> juvenile) vs. direct development (embryo -> juvenile), radial vs. spiral cleavage, blastomeres

Cell Cleavage Stages
1. Pattern depends on yolk content
2. Little yolk = holoblastic
3. Radial (urchins) vs. spiral (nemerteans)
4. Detailed fate maps are feasible

b) Blastulation

Key Terms: blastula, blastocoel

IV. Gastrulation and the Formation of Germ Layers

Key Terms: invagination, germ layers, ecto- vs. meso- vs. endoderm, diploblastic vs. triploblastic

a) Formation of the Coelom

Key Terms: schizocoely vs. enterocoely

V. Mechanisms of Development
Links to Pattern Formation Labs

a) Nuclear Equivalence (skim)

b) Cytoplasmic Specification (Skim, study Fig. 8-14)

Key Terms: mosaic vs. regulative development

Separate embryos at 4 cell stage:
Urchin: Result is 4 miniature larvae
Mollusc: Result is abnormal larvae
Conclusion: Urchin cells are less fixed in their fate

c) Embryonic Induction

Key Terms: primary organizer, primary vs. secondary induction

PrimaryOrganizer:
1. Location in embryo matters
2. Proximity to other cells matters
3. Certain regions contain “primary organizer”
4. Can experimentally make embryo with two backbones

d) Gene Expression during Development (Study Figs. 8-16, 8-17, 8-18)
Links to "Evo Devo" (Evolution and Development) Labs or Here

Key Terms: homeotic genes, homeobox, homeodomain

Study this section. We will come back to it later in the course and it will help to read it now.

VI. Vertebrate Development (in part)

a) The Common Vertebrate Heritage

b) Amniotes and the Amniotic Egg (will cover later)

VII. Development of Systems and Organs (skip)

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or back to Chapter 7
or ahead to Chapter 11