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Principles of Biology, 21 April 2009

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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

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