Fig. 6. FISH analysis of homologue pairing during meiotic time courses of wild-type (2n WT) and sir3 (2n sir3D) SK1 strains. Cosmid probe h, which maps near centromere XI (Trelles-Sticken et al., 2000), was hybridized to spread preparations obtained at various times after transfer to sporulation medium (Minutes in SPM). Pairing values (%) reflect the proportion of nuclei containing cosmid signals that touched each other or showed an enlarged coalesced signal. More than 100 FISH signal pairs were scored per time point and strain. The frequencies of nuclei with paired signals increased more gradually in the absence of Sir3p, reaching nearly wild-type levels with a 3 hour delay. In the wild type, maximal signal pairing values were reached at 300 minutes and remained nearly constant up to 420 minutes The occurrence of meiotic divisions after 240 minutes and 300 minutes in 2n WT and 2n sir3D meiosis, respectively, might explain why pairing values never exceeded 60%.