Meiosis I in human oocytes

Oocytes aspirated from women undergoing laparoscopic sterilisation were matured in vitro from the germinal vesicle stage. They showed that germinal vesicle breakdown spanned a period of about 12 h; the oocytes were at diakinesis by 12 h, and at metaphase I by 16 h where they remained for a further 10-12 h. Anaphase I took place after about 26 h. The meiotic preparations lacked the clarity of chromosome definition seen in mouse oocytes and accurate chiasma counts could not be made. However univalents at first meiotic metaphase could be detected without ambiguity and were found in women significantly older than those whose metaphase I oocytes contained bivalents only.