ytEx209 contains [pRM8 (mel-46+) + pTG96(sur-5::GFP)]. GFP minus worms are Mel or sterile at 25 C (completely penetrant). Strong but not fully penetrant Mel at 15 C. Culture at 20°C or higher in order not to lose the transgene. To start a yt5 homozygous culture transfer several GFP minus worms to 15°C.