Practice question

Early chick axis establishment involves subtle bioelectric differences rather than simple genetic prepattern alone. Measurements show posterior marginal cells exhibit distinct intracellular pH elevation and depolarized membrane potential regulating beta-catenin nuclear transport and Vg1 exocytosis. These electrochemical gradients influenced by gravity during egg rotation in albumen and shell create biased Wnt8c and Nodal expression posteriorly. Subsequent feedback through Wnt, FGF and TGF-beta reinforces dorsoventral and anteroposterior polarity. While genes elaborate pattern, initial bias linked experimentally to pH and membrane potential asymmetry across blastoderm, not solely gravity or genetic factors alone.