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| the early developmental stage of an animal, following the morula stage and consisting of a single, spherical layer of cells enclosing a hollow, central cavity. |
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| a metazoan embryo in an early state of germ layer formation following the blastula stage, consisting of a cuplike body of two layers of cells, the ectoderm and endoderm, enclosing a central cavity, or archenteron, that opens to the outside by the blastopore: in most animals progressing to the formation of a third cell layer, the mesoderm. |
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| a mature sexual reproductive cell, as a sperm or egg, that unites with another cell to form a new organism. |
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| the cavity of a blastula, arising in the course of cleavage. |
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| any cell produced during cleavage. |
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| the union of male and female gametic nuclei |
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| the cell produced by the union of two gametes, before it undergoes cleavage. |
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| group of related genes that determine the basic structure and orientation of an organism. |
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| gene involved in the early stages of pattern formation that define repeated units in a segmented organism, usually the embryo. |
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| refers to the uneven distribution of yolk in the cytoplasm of ovums found in birds, reptiles, fish, and monotremes. |
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| refers to the even distribution of yolk in the cytoplasm of ovums of mammals and other vertebrates |
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| describes the placement of the yolk in the centre of the cytoplasm of ovums. |
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| having an intermediate amount of yolk. |
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| a very small amount of yolk. |
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| refers to the uneven distribution of yolk in the cytoplasm of ovums. |
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| is a process by which some animal embryos develop. |
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| is a process by which some animal embryos develop |
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| to polyspermy involves the opening of Na+ channels in the egg plasma membrane |
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| Hierarchy of Developmental Decisions |
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| couldn't find a specific definition. |
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| is the process by which a less specialized cell becomes a more specialized cell type |
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| there is no distinctive larval stage. |
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| In many (probably most) animals, the embryo develops into a larva. A larva is a sexually-immature animal that is distinctly different in form from its parents. Because they’re so different from their parents, larvae rarely eat the same foods; indeed, the larvae of a given species may live in entirely different habitats than do the adults. |
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| is an opening into the archenteron during the embryonic stages of an organism |
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| is the division of cells in the early embryo |
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| describes an egg that has been fertilized by more than one sperm |
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| undergoing cleavage in which the entire zygote participates; dividing completely. |
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| partially dividing; undergoing cleavage in which only part of the zygote participates. |
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| The first meiotic division has started (dark area in the lower part of the egg), while the sperm pronucleus can still be seen (dark area in the upper middle part of the egg). Note the fertilization membrane and associated layers. |
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| is a distinct juvenile form many animals undergo before metamorphosis into adults. |
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| contains large yolky cells that divide very slowly, in contrast with the animal pole above it. |
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| consists of small cells that divide rapidly, in contrast with the vegetal pole below it. |
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| consists of small cells that divide rapidly, in contrast with the vegetal pole below it. |
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| Derived from two embryonic germ layers, the ectoderm and the endoderm |
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| couldn't find a definition? |
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| is one of the three primary germ cell layers in the very early embryo |
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| is one of the three primary germ cell layers in the very early embryo. |
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| is one of the three primary germ cell layers in the very early embryo |
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| any member of the lower invertebrate phyla in which the mouth appears before the anus during development |
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