Spo11p is a key mediator of interhomolog interactions during meiosis. Deletion of the SPO11 gene decreases the length of S phase by approximately 25%. Rec8p is a key coordinator of meiotic interhomolog and intersister interactions. Deletion of the REC8 gene increases S-phase length, by approximately 10% in wild-type and approximately 30% in a spo11Delta background. Thus, the progression of DNA replication is modulated by interchromosomal interaction proteins. The spo11-Y135F DSB (double strand break) catalysis-defective mutant is normal for S-phase modulation and DSB-independent homolog pairing but is defective for later events, formation of DSBs, and synaptonemal complexes. Thus, earlier and later functions of Spo11 are defined. We propose that meiotic S-phase progression is linked directly to development of specific chromosomal features required for meiotic interhomolog interactions and that this feedback process is built upon a more fundamental mechanism, common to all cell types, by which S-phase progression is coupled to development of nascent intersister connections and/or related aspects of chromosome morphogenesis. Roles for Rec8 and/or Spo11 in progression through other stages of meiosis are also revealed.