The re-formatoin of the nuclear envelope during M-phase of the cell cycletakes place during telophase. The nuclear membrane which disappears during prophase reappears in the telophase. But before it is reformed the nucleus gets reorganised by decondensation from chromosome and reassembly of the nuclear lamina. Related Theory Crossing over occurs between prophase I and metaphase I (pachylene stage) and is the process where two homologous non-sister chromatids pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.