Practice question

Mammalian zona pellucida is functionally analogous to vitelline envelope surrounding eggs of sea urchins and other invertebrates. Both are extracellular coats composed of sulfated glycoproteins synthesized during oogenesis, mediate species-specific sperm attachment, induce acrosome reaction, and undergo cortical granule-driven modifications resulting in hardening and fertilization envelope elevation. In mammals zona hardens via ovastacin cleavage of ZP2 and zinc crosslinking; in invertebrates vitelline envelope elevates forming permanent block. Analogy reflects evolutionarily conserved strategy regulating gamete interaction, preventing pathological polyspermy and triploid formation during fertilization events.