[Cytological research on the argentophilic nucleolus-organizer regions of the metaphase chromosomes in parthenogenetic mouse embryos].

Silver staining technique visualizing argentophilic nucleolus organizer regions (Ag-NORs) was used for studying parthenogenetic mouse embryos produced by artificial activation of oocytes in Ca(2+)-Mg(2+)-free medium. Ag-NOR-containing chromosomes were detected in metaphases of parthenogenetic embryos during six successive cleavage divisions starting with the two-cell stage. The frequency of metaphases with varying AG-NOR number in diploid parthenogenones was similar to that in the control (fertilized) embryos. Average number of metaphase Ag-NOR chromosomes (calculated per diploid chromosome set) in haploid parthenogenones exceeded that in the control; in some cases all NORs were stained by silver. This is evidence that latent ribosomal cistrons in some chromosomes can be activated.