What phase of meiosis do oocytes remain arrested in for the majority of a woman's reproductive years?

Oocytes are arrested in Prophase I of meiosis for the majority of a woman's reproductive years. This arrest allows the oocytes to be maintained in a dormant state until the woman reaches puberty and begins to ovulate. During this time, each menstrual cycle will typically lead to the maturation and release of a single oocyte, which then completes the first meiotic division just prior to ovulation, progressing to Metaphase II.

In Prophase I, oocytes undergo a process known as diplotene, where they can remain for years; this is the longest phase of meiotic prophase and is characterized by the pairing of homologous chromosomes, and the crossing over of genetic material takes place before they are arrested. This prolonged arrest is a defining feature of female gametogenesis, which contrasts with the continual process of spermatogenesis in males, where sperm cells are produced throughout the male reproductive life without such an extended arrest.

Recognizing that the oocyte remains in this arrested state until developmental cues prompt the resumption of meiosis is essential for understanding female reproductive biology and the implications it has for fertility and age-related changes in reproductive capability.