Human proteome contains 25 selenoproteins. Selenocysteine, sometimes called the “twenty-first amino acid,”

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If the P2 cell is killed at the early 4-cell stage, the ABp cell does not generate its normal complement of cells

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Cleavage type- Unequal radial holoblastic cleavage

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Cortical Rotation The cortical cytoplasm has rotated 30º relative to the internal cytoplasm.

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Gray Crescent 

The region opposite the point of sperm entry, where the greatest displacement of cytoplasm occurs (Gastrulation will begin)

Vegetal rotation: Vegetal cells asymmetrically press up against the inner blastocoel roof on the dorsal side.

Bottle cell formation and invagination: Localized apical constriction at the dorsal blastopore lip creates anisotropic forces that foster invagination.

Involution and cell migration: The leading edge of invaginating cells crawls up onto the blastocoel roof.

Convergence and extension: The targeted medial-to-lateral intercalation of cells on the midline (convergence) drives anterior-posterior axis elongation (extension).

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Amphibian Gastrulation