Polymitotic: supernumerary repetitions of meiosis Il

V. Ambros and H. R. Horvitz (Science 226:409, 1984), in their analysis of cell lineages in the nematode Caenorhabditis elegans, have found mutations that cause supernumerary moltings or repetitions of other developmental programs. The maize mutant polymitotic causes supernumerary divisions of meiocytes. We suggest (West, Ph.D. thesis, Univ. of Minn., 1985) that polymitotic (po) and the lin mutants of C. elegans share the common characteristic of affecting genetic switches which control developmental subroutines. Mutation results in recycling of the program.

In the case of polymitotic, the events of meiosis II repeat several times. Immediately upon telophase II, chromosome condensation recommences, followed by spindle formation and cytokinesis. Each cycle is very rapid. Lacking chromosome duplication (as meiosis II does), these polymitoses produce nonviable cell remnants, varying in size, and containing variable amounts of chromatin, with resulting male and female sterility. The term "megacyte" was suggested for megaspore remnants observed replacing embryo sacs (West, M.S. thesis, Univ. of Minn., 1984), following Beadle's suggestion of the term "microcyte" for microspore remnants which replace pollen (G.W. Beadle, Cornell Ag. Exp. Stat. Mem. #135, 1932).

D.P. West and R.L. Phillips*

*Univ. of Minn.

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