meDf6; yDp15 is WT hermaphrodite which is Him. 23% of self-progeny are WT males. yDp15 recombines with X, but such recombination is greatly reduced in an meDf6 background. Maintain strain by picking L4 hermaphrodites and making sure they give lots of dead eggs and lots of males. [yDp15 XO males with an intact X chromosome are >90% inviable.]