Final answer:
The single layer of squamous cells around the egg differentiates into granulosa cells and proliferates during oogenesis. This results in the formation of secondary follicles and ultimately the release of a secondary oocyte surrounded by the zona pellucida and the corona radiata.
Step-by-step explanation:
During oogenesis, the single layer of squamous cells that surround the egg undergoes differentiation into granulosa cells and proliferation into multiple layers. The primary follicles start with a single layer of granulosa cells, which then transition from flat or squamous to a more cuboidal shape, and begin to proliferate as the follicles grow. This process results in what are known as secondary follicles, eventually leading to the development of a tertiary follicle that will release the secondary oocyte during ovulation.
The zona pellucida is a thick glycoprotein membrane that forms just outside the oocyte's plasma membrane, and it plays a crucial role in fertilization. The corona radiata, a layer of granulosa cells, surrounds the zona pellucida and the oocyte itself, both providing additional protection and contributing to the necessary conditions for fertilization to take place.