NEW INSIGHTS INTO THE ROLE OF THE MAIZE AMEIOTIC1 LOCUS

In maize the am1-1 mutant allele results in both the male and female m eiocytes undergoing mitosis in place of the meiotic divisions. A secon d mutant allele am1-praI enables both the male and female meiocytes to proceed to the early zygotene stage of meiotic prophase I before bein g blocked. Here we report on three new alleles that allow all male mei ocytes to undergo mitosis but in female meiocytes approximately one qu arter (am1-2), one half (am1-485), or all (am1-489) of them are blocke d at an abnormal interphase stage. Previous analysis has shown that am 1-pra1 is dominant to am1-1 in male meiocytes. Cytological analysis of heteroallelic combinations in female meiocytes now indicates a domina nce relationship of am1praI > am1-1 > am1-2/am1-485 > am1-489. The evi dence provided by the female phenotypes of the new mutant alleles sugg est that, whereas the normal am1 allele is required for the meiocytes to proceed through meiosis, a partially functional allele may be requi red for their diversion into a mitotic division. The partial or comple te blockage of mitosis in female meiocytes carrying the new am1 allele s rules out the possibility that the mitotic division of mutant meiocy tes reflects a simple default pathway for cells that cannot initiate m eiosis. This locus may have a dual function.