To assess whether these MLH1/3 foci in Trip13Gt/Gt pachytene spermatocytes represent CO events completed to a point where they could maintain interhomolog attachments though the end of prophase I, we treated testicular cells from 17.5–20.5-d-old control (+/+), Trip13Gt/Gt, and Dmc1 −/− mice with the protein phosphatase inhibitor okadaic acid (OA), a chemical that induces degradation of the SC, chromosome condensation, and premature progression to metaphase I [33].