Practice question

After completing meiosis I and extruding first polar body following LH surge, mammalian secondary oocyte immediately enters meiosis II without DNA replication and arrests at metaphase II via cytostatic factor composed of Mos MAPK pathway maintaining high maturation promoting factor activity. Chromosomes align on meiotic spindle awaiting fertilization. Only sperm-induced calcium oscillations activate anaphase promoting complex, degrade cyclin B and securin, permitting chromatid separation and second polar body expulsion. Metaphase II arrest prevents parthenogenetic activation, ensures rapid zygote formation upon sperm entry, coordinates oocyte activation timing with fertilization and embryonic cell cycle progression.