Chapter 42 — Animal Development Study Materials Flashcards

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Determination

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The process by which a cell becomes committed to a specific fate even though it may not yet look or function like that cell type. Commitment occurs before visible differentiation and restricts future developmental options.

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Differentiation

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The process by which a cell physically and functionally becomes specialized through activation of specific genes and production of particular proteins. Differentiation results in changes in cell shape, structure, and function.

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Morphogenesis

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The physical shaping of the embryo driven by cell movements, folding, and rearrangement. It sculpts tissues and organs but does not necessarily change cell identity.

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Gastrulation

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The rearrangement of a blastula into a three-layered embryo that produces the ectoderm, mesoderm, and endoderm. A major outcome is formation of the primitive gut (archenteron) and establishment of the body plan.

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Polarity

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Uneven distribution of materials in the egg, such as yolk and localized mRNAs, which helps determine body axes like animal-vegetal and dorsal-ventral. Polarity influences subsequent cleavage patterns and cell fates.

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Animal Hemisphere

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The half of an egg containing the nucleus and relatively less yolk; its cells divide faster and typically give rise to ectoderm and much of the embryo's body. Cleavage is more rapid here than in the vegetal hemisphere.

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Vegetal Hemisphere

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The half of an egg that contains more yolk, causing slower cleavage divisions and often contributing to endoderm formation. Heavy yolk influences cleavage mechanics and fate.

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Gray Crescent

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A region in amphibian eggs that appears after sperm entry due to cortical rotation, marking the future dorsal side. It is essential for correct body-axis formation.

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Cortical Rotation

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A sperm-triggered shift of the egg's outer cytoplasm relative to inner cytoplasm guided by microtubules. This movement redistributes cytoplasmic determinants and helps establish the dorsal-ventral axis.

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Beta-catenin

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A transcriptional regulator that accumulates on the dorsal side of amphibian embryos and activates genes involved in forming the organizer. Its dorsal accumulation is protected from degradation.

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GSK-3

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An enzyme that normally targets beta-catenin for degradation; it is active on the ventral side of amphibian embryos. Inhibition of GSK-3 on the dorsal side allows beta-catenin to accumulate.

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Cleavage

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Rapid mitotic cell divisions following fertilization that partition the zygote into many blastomeres without increasing overall embryo size. Cleavage ends with formation of the blastula.

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Blastula

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A hollow ball of cells formed at the end of cleavage that contains a fluid-filled cavity called the blastocoel. The blastula stage sets the scene for gastrulation movements.

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Blastocoel

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The fluid-filled cavity inside the blastula that provides space for cell movements during gastrulation and helps position cells for later patterning.

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Blastocyst

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The mammalian form of the blastula that arises after about 32 cells and contains an inner cell mass (ICM) and a trophoblast, plus a fluid cavity. The ICM gives rise to the embryo proper while the trophoblast contributes to the placenta.

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Inner Cell Mass

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A cluster of cells inside the mammalian blastocyst that will form the embryo proper and later segregate into the epiblast and hypoblast. The epiblast produces the three germ layers.

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Primitive Streak

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A structure that forms on the surface of the epiblast in birds and mammals where cells ingress during gastrulation. It is functionally equivalent to the amphibian dorsal lip.

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Hensen's Node

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A thickened region at the anterior end of the primitive streak in birds and mammals that acts like an organizer to coordinate body-axis formation. It guides axial patterning and gastrulation movements.

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Neurulation

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The formation of the neural tube from ectoderm, where the neural plate folds inward and closes to form the central nervous system. Neural crest cells form at the edges and migrate to create diverse structures.

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Autonomous Specification

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A mode of cell fate determination in which cell fates are specified by inherited cytoplasmic determinants independent of neighbors. It is common in many invertebrates and can resist removal of the cell.