Cyclin A2 is not necessary for progression through MI. (a) Rates of GVBD in cyclin A2^fl/fl (n = 102) and cyclin A2^−/− (n = 106) groups. P > 0.05, by t test. Data is mean and SEM from four replicate experiments. (b) Rates of polar body extrusion (PBE) in cyclin A2^fl/fl (n = 92) and cyclin A2^−/− (n = 82) groups at different time points. P > 0.1, by t test. Data is mean and SEM from three replicate experiments. (c) MI oocytes from cyclin A2^fl/fl and cyclin A2^−/− mice showed apparently normal spindle structures confirmed in d by analysis of spindle length (top left), spindle width (top right), and chromosome alignment (bottom). No differences were detected between cyclin A2^fl/fl (n = 82) and cyclin A2^−/− (n = 91) groups. Error bars represent SEM. Bars, 10 µm. P > 0.1, by t test. (e) kt–mt attachments in cold-treated MI-stage oocytes from cyclin A2^fl/fl and cyclin A2^−/− mice. One example of each attachment type observed in MI-stage oocytes is shown. Bars, 10 µm. (f) Analysis of attachment types in oocytes from cyclin A2^−/− (1,019 attachments from 27 oocytes) and cyclin A2^fl/fl (839 attachments from 22 oocytes) mice. Colored surroundings of each box correspond to the colors in the quantification of attachment types in each bar. Arrows indicate the kinetochore pair with the described attachment. Bars, 2 µm. P > 0.1 by χ² test.