Fig. 9. Summary of meiotic and developmental defects observed in mat-1 hypomorphs. Under semi-permissive temperatures (rows 1-3), three different classes of meiotic and developmental phenotypes are observed for mat-1 mutants: normal meiosis (top row), the 2PB class (row 2), and the 1PB class (row 3). In the 2PB class, both MI and MII defects occur, leading to asymmetric but more synchronous divisions in the two- to four-cell stage. In the 1PB class, MI defects occur, MII is skipped, and meiotic exit defects are apparent. These defects lead to a symmetric first cleavage and a synchronous second mitosis in which the orientations of divisions are abnormal. Eggshell formation is also defective. In the fully restrictive conditions (row 4), all embryos arrest at metaphase of MI and make weak, incompletely hardened eggshells.

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