Oogenesis. Germinal cells mature into diploid primary oocytes. Every 28 days starting at puberty, one primary oocyte undergoes meiosis I. One of the haploid daughter cells is a nonfunctional polar body; the other (secondary oocyte) grows in a follicle and is released (ovulation). Meiosis II occurs only if the secondary oocyte is fertilized by a sperm, producing an ovum and another polar body. Review: