Plasmid segregation during meiosis I. (A and B) The segregation of fluorescence-tagged STB and ARS (lacking a partitioning system) reporter plasmids (Mehta et al., 2002; Cui et al., 2009) was scored in [cir+] diploid cells by counting plasmid foci in each daughter nucleus at the end of meiosis I. Bars, 2 µm. (C) In the bar graph representation, the n:n and n:n − 1 classes denote equal (or nearly equal) plasmid segregation; the n:n′ and n:0 classes denote missegregation and segregation failure, respectively. There is some uncertainty in these numbers as foci occasionally tend to overlap and the number of plasmid molecules in each focus is unknown. The mean number of plasmid foci per nucleus for each segregation class is given below the graphs. These data represent 80 and 90 binucleate cells analyzed for the STB and ARS plasmids, respectively. The error bars indicate ± SEM.