Colcemid-treated oocytes are arrested in metaphase II. (A) A representative colcemid-treated (50 µM) oocyte karyotyped 3 h after GVBD, stained with Sytox orange and anti–Aur-B (n = 9). The inset depicts a single dyad. (B) A colcemid-treated (50 µM) oocyte was imaged live, beginning at 3 h after GVBD (00:00). The oocyte was then exposed to UV excitation until the end of the imaging experiment. The oocyte was pricked immediately after the scan at 00:16. The schematic depicts position of the spindle/chromosomes in a live oocyte. Note that the egg chromosomes at 00:53 would be forming the female pronucleus and be beyond the depth of the confocal imaging system. See Video 2 for the entire series.