Fig. 1

Oogenesis and follicular development. Meiosis occurs, following the mitotic proliferation of oogonia. The oogonia first enters the leptotene. stage of the first meiotic prophase and becomes the primary oocyte. Before birth, the development of primary oocytes stagnates at the zygotene and pachytene stages.Shortlyafter birth, the oocyte enters the diplotene stage. At this moment, the oocyte has a large nucleus, known as germinal vesicle, and gradually forms a primary follicle. Oocytes at this stage are diploid but have four times as much DNA as haploid cells. During this period, the development of oocytes will keep stagnant for a long time, allowing homologous chromosomes to fully perform the transcription of maternal mRNA