Animal developmentPrinciples 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

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

Figure 8-7

From:

Hickman et al. 2006 (13th ed.)

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

Direct development

Embryo develops into adult-like individual

Indirect development

Embryo develops into larval stage

May be several intermediate stages before adult