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Chapter 47 - animal development


fertilized egg


the idea that the egg or sperm contains an embryo - a preformed miniture infant, or "homunculus"


the form of an animal emerges gradually from a relatively formless egg

cytoplasmic determinants

the material substances in the egg that influence the course of early development by regulating the expression of genes that affect the developmental fate of cells

cell differentiation

the specialization of cells in their structure and function; dependent on the control of gene expression


the process by which an animal takes shape and the differentiated cells end up in the appropriate locations

three successive stages that begin to build the animal's body

cleavage, gastrulation, organogenesis


a hollow ball of cells- blastula- is created by rapid cell division; the embryo does not enlarge during this period of development.


three-layer embryo - gastrula


rudimentary organs from which adult structures grow


union of gamates (egg and sperm)

acrosomal reaction

the discharge of a sperm's acrosome when the sperm approaches the egg


a vesicle at the tip of a sperm cell that helps the sperm penetrate the egg

cortical reaction

exocytosis of enzymes from cortical granules in the egg cytoplasm during fertilization

slow block to polyspermy

the formation of the fertilization envelope and other changes in the egg's surface that prevent fusion of the egg with more than one sperm

fast block to polyspermy

the depolarization of the egg membrane within 1-3 seconds after sperm binding to the vitelline layer; prevents additional sperm from fusing with the egg's plasm membrane

cortical granules

vesicles located just under the plasm membrane of an egg cell that undergo exocytosis during the cortical reaction

fertilization envelope

transformation of the viteline layer

zona pellucida

extrcellular matrix of the egg


small cells of the early embryo


the fluid-filled cavity that forms in the center of the blastula embryo


the hollow ball of cells marking the end stage of cleavage during early embryonic development


an embryonic cap of dividing cells resting on a large undivided yolk


the endoderm-lines cavity, formed during the gstrulation process, that develops into the digestive tract of an animal


the opening of thr archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes


an embryoninc stage in mammals; a hollow ball of cellspreduced one week after fertilization in humans


a thin, pigmented inner layer of the vertebrate eye


the innermost of four extraembryonic membranes; encloses a fluiod-filled sac in which the embryo is suspended


one of four extraembryonic membranes; serves as a repository for embryo's nitrogenous waste

convergent extension

a mechanism of cell crawling in which cells of a tissue layer rearrange themselves in such a way that the sheet of cells becomes narrower while it becomes longer

cell adhesion molecules (CAMs)

glyoproteins that contribute to cell migration and stable tissue structure

apical ectodermal ridge

a limb-bud organizer region consisting of a thickened area of ectoderm at the tip of a limb bud

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