a, Germline elimination by treating WT C. elegans with 5-fluoro-2′-deoxyuridine (FUDR) or by using the gon-2(q362ts) allele at the restrictive temperature. Differential interference contrast images of day-3 adults are shown. b, Mitoflash frequencies (means ± s.e.m.) of WT, FUDR-treated WT, and gon-2(q362ts) mutant worms on adult days 1–5 (n = 15 worms). All animals were cultured at 27 °C until the late larval stage 2 or early larval stage 3 before being moved to 25 °C, at which point half of the WT animals were cultured on plates containing 100 μg ml−1 FUDR. The worms were checked for the presence or absence of a germline before imaging for mt-cpYFP.