Fig. 4. Distribution of nuclei in wild-type and mdy2 mutant zygotes 5.5 hours after initiation of mating. The mating mixtures were incubated for 5.5 hours on YPD plates, and the cells were stained with DAPI. Fields of cells containing zygotes were photographed at random for analysis, and the positions of the nuclei were determined. We categorized zygotes according to nuclear positions into one of three classes: pre-nuclear fusion zygotes (class I, top), post-nuclear fusion zygotes (class II, centre), and `zygotes' in which the haploid nuclei had undergone mitotic division (class III, bottom). 100 zygotes were counted for each cell type.