Cyclin A2 is necessary to prevent a high rate of abnormal kt–mt interactions in MII-stage oocytes. Representative images of kt–mt attachments in cold-treated control and cyclin A2 knockout oocytes fixed at 12.5 h after hCG as oocytes reach MII (a) and at 14.5 h after hCG when oocytes have arrested at the mature MII stage. Arrow shows stabilized non-kMT. (c). (a and c, insets) Examples of different attachment types (5 shows normal polar attachment; 2 and 6 show lateral attachments; 3, 4, and 8 show examples of attachments in nonspindle chromosomes and microspindles; and 1 and 7 show merotelic attachments). Bars: (yellow) 10 µm; (orange) 2 µm. Analysis of the different attachment types at 12.5 h (b) and 14.5 h (d) in cyclin A2^fl/fl oocytes (n = 11 and 19, respectively) and cyclin A2^−/− oocytes (n = 14 and 16, respectively). Numbers in parentheses represent total number of attachments examined. Note the increase in lateral and merotelic attachments and the delay in establishing polar attachments in cyclin A2^−/− oocytes. ***, P < 0.001. Data on attachment types were pooled from the indicated number of oocytes and analyzed using a χ² test.