Principles of Biology, 21 April 2009 Animal development Principles of Biology, 21 April 2009 Donald Winslow References: Hickman, Cleveland P.; et al. 2008. Integrated Principles of Zoology, 14th ed., McGraw-Hill, NY., Chapter 8. Mader, Sylvia S. 2007. Biology, 9th ed., McGraw-Hill, NY., Chapter 44.

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

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.

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

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

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

From: Hickman et al. 2006 (13th ed.)‏ Figure 8-7

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

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

Figure 08.10 From Hickman et al. 2006 (13th ed.)‏

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

Neurulation Nervous system forms from ectoderm Induction by adjacent cells

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