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| The discharge of a sperm’s acrosome when the sperm approaches an egg. |
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| A vesicle at the tip of a sperm cell that helps the sperm penetrate the egg. |
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| One of four extraembryonic membranes; serves as a repository for the embryo’s nitrogenous waste. |
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| The innermost of four extraembryonic membranes; encloses a fluid-filled sac in which the embryo is suspended. |
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| Member of a clade of tetrapods that have an amniotic egg containing specialized membranes that protect the embryo, including mammals and birds and other reptiles. |
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| The portion of the egg where the least yolk is concentrated; opposite of vegetal pole. |
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| The endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal. |
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| The fluid-filled cavity that forms in the center of the blastula embryo. |
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| An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans. |
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| An embryonic cap of dividing cells resting on a large undivided yolk. |
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| A small cell of an early embryo. |
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| The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes. |
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| The hollow ball of cells marking the end stage of cleavage during early embryonic development. |
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| An important class of cell-to-cell adhesion molecules. |
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| The structural and functional divergence of cells as they become specialized during a multicellular organism’s development; dependent on the control of gene expression. |
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| The outermost of four extraembryonic membranes; contributes to the formation of the mammalian placenta. |
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| Exocytosis of enzymes from cortical granules in the egg cytoplasm during fertilization. |
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| The maternal substances in the egg that influence the course of early development by regulating the expression of genes that affect the developmental fate of cells. |
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| Four membranes (yolk sac, amnion, chorion, allantois) that support the developing embryo in mammals and birds and other reptiles. |
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| Territorial diagram of embryonic development that reveals the future development of individual cells and tissues. |
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| Three main layers that form the various tissues and organs of an animal body. |
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| A type of cleavage in which there is complete division of the egg, as in eggs having little yolk (sea urchin) or a moderate amount of yolk (frog). |
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| A cluster of cells in a mammalian blastocyst that protrudes into one end of the cavity and subsequently develops into the embryo proper and some of the extraembryonic membranes. |
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| A type of cleavage in which there is incomplete division of yolk-rich egg, characteristic of avian development. |
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| The development of body shape and organization. |
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| A solid ball of blastomeres formed by early cleavage. |
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| A band of cells along the border where the neural tube pinches off from the ectoderm. The cells migrate to various parts of the embryo and form the pigment cells in the skin, bones of the skull, the teeth, the adrenal glands, and parts of the peripheral nervous system. |
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| The development of organ rudiments from the three germ layers. |
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| A groove on the surface of an early avian embryo along the future long axis of the body. |
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| Paired blocks of mesoderm just lateral to the notochord of a vertebrate embryo. |
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| Describing a cell that can give rise to all parts of an organism. |
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| The outer epithelium of the blastocyst, which forms the fetal part of the placenta. |
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| The portion of the egg where most yolk is concentrated; opposite of animal pole. |
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| Nutrients stored in an egg. |
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| One of four extraembryonic membranes that support embryonic development; the first site of blood cells and circulatory system function. |
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| The extracellular matrix of a mammalian egg. |
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| zone of polarizing activity (ZPA) |
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Definition
| A limb-bud organizer region consisting of a block of mesoderm located where the posterior side of the bud is attached to the body. |
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