Practice question

Early avian dorsal-ventral polarity before gastrulation linked to bioelectric patterns across blastoderm. Measurements show potential difference and intracellular pH gradient between dorsal epiblast and ventral hypoblast established during egg rotation in oviduct, mediated by ion transporters H+ V-ATPase and Na+/K+ ATPase. Depolarization of embryonic side elevates beta-catenin. Gravity and primitive streak act later. Experimental equalization of membrane potential ventralizes embryos. Therefore initial dorsal-ventral axis depends on egg membrane potential and pH differences rather than solely gravity or primitive streak itself. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.