The unfertilized egg can now be activated by three different approaches, all of them leading to a decrease in intracellular zinc availability. The first is through the physiological pathway, fertilization (center row). This induces calcium oscillations in the egg, leading to the zinc sparks and subsequent cell cycle resumption. The two other approaches induce parthenogenesis and are pharmacological, either using modulators of intracellular calcium (top arrow) or zinc (bottom arrow). The calcium-based approaches induce zinc sparks, while the zinc-based approach bypasses the need for calcium oscillations by directly decreasing the availability of zinc in the egg (green box). Furthermore, cell cycle arrest at metaphase can be reestablished by raising zinc availability (red box), thus implicating zinc as a central regulator of the cell cycle during oocyte maturation and fertilization.