The Spindle Pole Body (SPB) Duplication Cycle. (a) During G1 (prior to START), the distal end of the half-bridge (red) of the mother SPB (green) acquires a satellite (blue oval). (b) As cells traverse START, the satellite enlarges to form the daughter SPB (blue rectangle). (c) At late S phase, the bridge is severed and (d) the SPBs move apart to form a short spindle. (e) During mitosis, the spindle poles move further apart as the spindle elongates. (f) At the end of the cycle after spindle disassembly, each cell acquires a SPB.