when does a mature oocyte complete meiosis i?

A mature oocyte completes meiosis I just before ovulation , specifically after the LH surge and during oocyte maturation in the Graafian follicle , when the first polar body is extruded.

Quick Scoop

• In most female mammals, primary oocytes are arrested in prophase I from before birth until puberty.

• Just prior to ovulation, the luteinizing hormone (LH) surge triggers the resumption of meiosis and progression to metaphase I , followed by completion of meiosis I with extrusion of the first polar body , leaving the cell as a secondary oocyte.

• The mature oocyte (secondary oocyte) then arrests again at metaphase II and only completes meiosis II upon fertilization , if that occurs.

Most concise one‑line answer

A mature oocyte completes meiosis I around the time of ovulation , after the LH peak , when it exits prophase I and extrudes the first polar body.