Oogonia are diploid germ line cells that are precursor ova cells. They are produced during a process called oocytogenesis before and sometimes shortly after birth; there are believed to be a finite number of oogonia in each female at the time of birth.

Primary oocytes are diploid germ line cells that form from oogonia. Primary oocytes are immature ova. In order to develop further, primary oocytes enter into ootidogenesis, or meiosis to produce secondary oocytes. This process is arrested at prophase I late in fetal development. The period of arrest during ootidogenesis is called the dictyate stage and is characterized by a lack of cellular translation. This arrest is caused by blocked mRNA binding sites, which prevents translation initiation factors from binding. The dictyate stage ends before puberty by an increase in the secretion of luteinizing hormone (LH). 

Ootidogenesis is the production of secondary ooctyes from primary ooctyes through meiosis. Ootidogenesis features two periods of developmental arrest—dictyate—during the prophase I stage of meiosis I and during metaphase II of meiosis II. The dictyate stage of arrest ends at the onset of puberty due to a spike in luteinizing hormone (LH) levels. Ootidogenesis then continues until the second arrest period during metaphase II. This period ends at fertilization and allows the completion of ootidogenesis.

Secondary oocytes are haploid cells that are produced by primary oocytes through meiosis in a process called ootidogenesis. Secondary oocytes remain arrested in the metaphase II stage of meiosis until fertilization, when ootidogenesis is completed. The process of ootidogenesis also produces polar bodies.

Polar bodies are haploid cells produced during ootidogenesis. They are smaller than secondary oocytes due to asymmetric cell division. During asymmetrical cell division a smaller volume of cytoplasm is partitioned into the polar bodies than to the secondary oocytes. This makes polar bodies not viable for fertilization. Polar bodies are often degraded, but they can also remain in the human body.

Oogenesis, or the formation of egg cells, takes place in the ovaries. Specifically, oogenesis takes place in the follicles—a pack of cells surrounding developing oocytes that is located within the ovaries.

Follicles are packs of somatic cells that surround developing oocytes in the ovaries. Follicles develop through a process called folliculogenesis that occurs in tandem with oogenesis. At birth, women have all of their follicles; however, this number decreases as women age due to double stranded breaks in the DNA of primary oocytes contained within primordial follicles.

Folliculogenesis is the process of follicle development, which occurs simultaneously with oogenesis. The initial stage of follicle development is when dormant primordial follicles are formed prior to birth. Primordial follicles are composed of simple layers of cells. The exit from dormancy and initiation of further development is controlled by a complex interplay of hormones. During folliculogenesis, mitotic cell divisions and hormones promote development and increase the complexity of follicles.

Mature follicles contain two cell layers, theca cells and granulosa cells, which are formed during folliculogensis. Granulosa cells are present from the primordial follicle stage onwards and become surrounded by theca cells during the secondary follicle stage. After ovulation, theca cells secrete androgens and progesterone while granulosa cells secrete estrogen and progesterone.

Ovulation is the release of an oocyte from the follicle for fertilization. Upon release, the oocyte is a secondary oocyte arrested in the metaphase II stage of meiosis until fertilization.