1. Principles of Biology, 21 April 2009
Animal development
Principles of Biology, 21 April 2009
Donald Winslow
References:
Hickman, Cleveland P.; et al Integrated Principles of Zoology, 14th ed., McGraw-Hill, NY., Chapter 8.
Mader, Sylvia S Biology, 9th ed., McGraw-Hill, NY., Chapter 44.

2. Development Mechanisms of cellular differentiation Fertilization
Cleavage
Blastulation
Gastrulation
Neurulation
Direct development and indirect development

3. Mechanisms of cellular differentiation
Cytoplasmic localization
Gradients of molecules within cells determine developmental fate of daughter cells.
Induction
Adjacent cells determine the developmental fate of a cell.

4. Fertilization and activation
Prevention of polyspermy
Fast block
Change in membrane potential.
Slow block
Cortical reaction causes vitelline membrane to separate from cell membrane.

5. The Zygote Gray crescent Polarity Yolk
Shows orientation of embryo within zygote
Polarity
Animal and vegetal poles
Yolk
Provides nutrition for developing embryo

6. Patterns of cleavage Superficial cleavage
Ecdysozoan protostomes
(nematodes, arthropods, etc)‏
Radial cleavage—primitive deuterostomes
Discoidal meroblastic cleavage
Reptiles, birds, most fishes
Rotational holoblastic cleavage—mammals
Mosaic vs regulative cleavage

7. From:
Hickman et al (13th ed.)‏
Figure 8-7

8. Blastulation Blastula made up of blastomeres
Inner cavity is called “blastocoel”

9. Gastrulation Germ layer formation Coelom formation
Schizocoely (protostomes; e.g. earthworm)‏
Enterocoely (deuterostomes; e.g. lancelet)‏
Fate of blastopore (or primitive streak)‏
Protostomes: blastopore becomes mouth
Deuterostomes: blastopore becomes anus

10. Figure 08.10
From Hickman et al (13th ed.)‏

11. Extraembryonic membranes
Present in amniotic vertebrates
Reptiles, birds, mammals
Help embryo conserve water
Amnion, chorion, allantois

12. Neurulation Nervous system forms from ectoderm
Induction by adjacent cells

13. Direct and indirect development
Embryo develops into adult-like individual
Indirect development
Embryo develops into larval stage
May be several intermediate stages before adult