Gastrulation begins when a groove with raised edges called the ________ appears on the dorsal surface of the embryonic disc.

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The primitive streak is a groove with raised edges that appears on the dorsal surface of the embryonic disc during gastrulation. It is the site where cells will begin to migrate and differentiate into the three germ layers, ultimately forming the various body systems and structures in the developing embryo. The notochord, placenta, and spinal cord are all important structures in embryonic development, but they do not directly initiate gastrulation.

Gastrulation Begins When a Groove with Raised Edges Called the ________