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| a 180 nucleotide sequence within homeotic genes and some other developmental genes that is widely conserved in animals |
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| any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants and fungi by controlling the developmental fate of groups of cells |
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| a subset of homeotic genes |
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| a hallow ball of cells that marks the end of the cleavage stage during early embryonic development in animals |
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| the fluid-filled cavity that forms in the center of a blastula |
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| an embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm and endoderm |
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| in animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula |
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the innermost of the three primary germ layers in animal embryos;
lines the archenteron and gives rise to the liver, pancreas, lungs and the lining of the digestive tract in species that have these structures |
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the middle primary germ layer in a triploblastic animal embryo;
develops into the notochord, the lining of the coelom, muslces, skeleton, gonads, kidneys and most of the circulatory system in species that have these structures |
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the outermost of the three primary germ layers in animal embryos
gives rise to the outer covering and, in some phyla, the nervous system, inner ear and lens of the eye |
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| in a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and mouth in protostomes |
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| body symmetry in which a central longitudianl plane divides the body into two equal but opposite halves |
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| symmetry in which the body is shaped like a pie or barrel (lacking a left and right side) and can be divided into mirror-image halves by any plane through its central axis |
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| pertaining to the top of an animal with radial or bilateral symmetry |
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| pertaining to the underside, or bottom, of an animal with radial or bilateral symmetry |
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| pertaining to the rear, or tail end, of a bilaterally symmetrical animal |
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| pertaining to the front, or head, of a bilaterally symmetrical animal |
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an evolutionary trend toward the concetration of sensory equipment at the anterior end of the body
(formation of the head) |
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| a body cavity lined by tissue derived only from mesoderm |
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| sheets of tightly packed cells that line organs and body cavities as well as external surfaces |
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| animal tissue that functions mainly to bind and support other tissues, having a sparse population of cells scattered through an extracellular matrix |
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| tissue made up of neurons and supportive cells |
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| tissue consisting of long muscle cells that can contract, either on its own or when stimulated by nerve impulses |
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