Practice question

Amphibian dorsoventral axis established immediately after fertilization by sperm-induced cortical rotation. Sperm centriole nucleates microtubule array that transports dorsal determinants Dishevelled and GBP with plus-end kinesins to side opposite sperm entry, defining dorsal gray crescent enriched with beta-catenin stabilization factors. Gravity can bias rotation but primary cue is sperm entry point triggering cytoskeletal rearrangement. Genetic programs downstream including Wnt and Nodal refine axis but initial asymmetry derives from sperm entry triggering rotation rather than purely genetic preformation or blastocoel formation random position, linking fertilization site to organizer formation.