Ootidogenesis

The succeeding ootidogenesis is the step in which the primary oocyte turns into an ootid. It is achieved by meiosis. The primary oocyte is even defined from its role to undergo meiosis.

However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have taken this halt in development, called dictyate. First after menarche they continue to develop, although only a few does so every menstrual cycle.

Meiosis I
Meiosis I of ootidogenesis starts at embryonic age, but halts in diplotene of prophase I until puberty. For those primary oocytes continuing to develop in each menstrual cycle, however, synapsis occurs and tetrads form, enabling and crossing over. As a result of meiosis I, the primary oocyte becomes the secondary oocyte and the first polar body.

Meiosis II
Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this, too is halted in metaphase II. However, this only lasts until fertilization, if such occurs. When meiosis II is completed, an ootid and another polar body is created.