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Animal Development (Morphogenesis in animals involves specific changes in…
Animal Development
Morphogenesis in animals involves specific changes in cell shape, position, and survival
Morphogenesis is a major aspect of development in plants and animals, but only in animals does it involve cell movement.
During gastrulation, invagination is initiated by the wedging of cells on the surface of the blastula, but the movement of cells deeper into the embryo involves the extension of filopodia by cells at the leading edge of the migrating tissue.
The movements of convergent extension probably involve the extracellular matrix (ECM), a mixture of secreted glycoproteins lying outside the plasma membrane.
These cells produce a thickening called the primitive streak, which runs along what will become the bird’s anterior-posterior axis.
Clustered at one end of the blastocyst is a group of cells called the inner cell mass that develops into the embryo and contributes to all the extraembryonic membranes.
Amniote development includes the formation of four extraembryonic membranes: yolk sac, amnion, chorion, and allantois.
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Unique to vertebrate embryos is a band of cells called the neural crest, which develops along the border where the neural tube pinches off from the ectoderm.
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