| A | B |
|---|
| acrosomal reaction | discharge of a sperm’s acrosome when the sperm approaches an egg |
| acrosome | vesicle at the tip of a sperm cell that helps the sperm penetrate the egg |
| allantois | serves as a repository for the embryo’s nitrogenous waste. |
| amnion | encloses a fluid-filled sac in which the embryo is suspended |
| amniote | clade of tetrapods that have an amniotic egg containing specialized membranes that protect the embryo |
| animal pole | portion of the egg where the least yolk is concentrated |
| apical ectodermal ridge | limb-bud organizer region consisting of a thickened area of ectoderm at the tip of a limb bud |
| archenteron | endoderm-lined cavity formed during the gastrulation process develops into the digestive tract of an animal |
| blastocoel | fluid-filled cavity that forms in the center of the blastula embryo |
| blastocyst | hollow ball of cells produced one week after fertilization in humans |
| blastoderm | embryonic cap of dividing cells resting on a large undivided yolk |
| blastomere | small cell of an early embryo |
| blastopore | opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes |
| blastula | hollow ball of cells marking the end stage of cleavage during early embryonic development |
| cadherins | important class of cell-to-cell adhesion molecules |
| cell adhesion molecules (CAMs) | Glycoproteins that contribute to cell migration and stable tissue structure |
| cell differentiation | structural and functional divergence of cells as they become specialized |
| chorion | outermost of four extraembryonic membranes contributes to the formation of the mammalian placenta |
| cleavage | succession of rapid cell divisions without growth during early embryonic development |
| convergent extension | cell crawling in which the cells of a tissue layer rearrange themselves in such a way that the sheet of cells becomes narrower while it becomes longer |
| cortical granules | Vesicles located just under the plasma membrane of an egg cell that undergo exocytosis during the cortical reaction |
| cortical reaction | Exocytosis of enzymes from cortical granules in the egg cytoplasm during fertilization |
| cytoplasmic determinants | maternal substances in the egg that influence the course of early development by regulating the expression of genes |
| dorsal lip | dorsal side of the blastopore |
| ectoderm | gives rise to the outer covering and in some phyla the nervous system inner ear and lens of the eye |
| endoderm | ines the archenteron and gives rise to the liver pancreas lungs and the lining of the digestive tract |
| extraembryonic membranes | membranes (yolk sac |
| fast block to polyspermy | reaction prevents additional sperm from fusing with the egg’s plasma membrane |
| fate map | diagram of embryonic development that reveals the future development of individual cells and tissues |
| fertilization envelope | welling of the vitelline layer away from the plasma membrane |
| gastrulation | formation of a gastrula from a blastula |
| germ layers | Three main layers that form the various tissues and organs of an animal body |
| gray crescent | light-gray region of cytoplasm located near the equator of the egg on the side opposite the sperm entry |
| holoblastic cleavage | cleavage in which there is complete division of the egg |
| induction | ability of one group of embryonic cells to influence the development of another |
| inner cell mass | cluster of cells in a mammalian blastocyst that protrudes into one end of the cavity and subsequently develops into the embryo proper |
| invagination | infolding of cells |
| involution | cells rolling over the edge of the lip of the blastopore into the interior of the embryo during gastrulation |
| meroblastic cleavage | type of cleavage in which there is incomplete division of yolk-rich egg |
| mesoderm | develops into the notochord the lining of the coelom muscles skeleton gonads kidneys and most of the circulatory system |
| morula | development of body shape and organization |
| neural crest | band of cells along the border where the neural tube pinches off from the ectoderm |
| neural tube | tube of cells running along the dorsal axis of the body just dorsal to the notochord |
| notochord | long flexible rod that runs along the dorsal axis of the body in the future position of the vertebral column |
| organogenesis | development of organ rudiments from the three germ layer |
| pattern formation | ordering of cells into specific three-dimensional structures |
| positional information | indicating a cell’s location relative to other cells in an embryonic structure |
| primitive streak | groove on the surface of an early avian embryo along the future long axis of the body |
| somites | changes in the egg’s surface that prevent fusion of the egg with more than one sperm |
| totipotent | cell that can give rise to all parts of an organism |
| trophoblast | outer epithelium of the blastocyst which forms the fetal part of the placenta |
| vegetal pole | portion of the egg where most yolk is concentrated |
| yolk | nutrients stored in an egg |
| yolk plug | large food-laden endodermal cells surrounded by the blastopore of an amphibian gastrula |
| yolk sac | support embryonic development the first site of blood cells and circulatory system function |
| zona pellucida | extracellular matrix of a mammalian egg |
| zone of polarizing activity (ZPA) | organizer region consisting of a block of mesoderm located where the posterior side of the bud is attached to the body |
| morphogenesis | morphogenesis, development of body shape and organization |
| slow block to polyspermy | slow block to polyspermy, changes in the egg’s surface that prevent fusion of the egg with more than one sperm |
