Ovulated cyclin A2^−/− oocytes show abnormal MII-stage spindles. (a) After superovulation, cyclin A2^−/− and cyclin A2^fl/fl mice show no significant difference in the number of ovulated oocytes (n = 5 mice for each genotype). Error Bars represent SEM; P > 0.1 by t test. (b) Ovulated oocytes from the cyclin A2^−/− mice showed higher rates of spindle abnormality (37%, n = 71) than those from the cyclin A2^fl/fl group (2.9%, n = 105). ***, P < 0.001 by χ² test. The number in parentheses is the number of oocytes analyzed. (c) Examples of spindle phenotypes in ovulated oocytes from cyclin A2^fl/fl mice (top row) and cyclin A2^−/− mice (all other rows). The percentage of cyclin A2^−/− oocytes showing each named phenotype is provided. Arrow shows misaligned chromosomes. Bars, 10 µm.