DNA blot hybridization analysis of trRescueMu elements in grid G. Total DNA was prepared from individual grid G plants in rows 1 and 5, as listed at the top of the lanes; these rows represent two ears crossed by the same founder RescueMu pollen source. DNA samples were digested with HindIII, a unique site 0.5 kb from the internal end of the left TIR of the RescueMu element, and the resulting gel blot was hybridized with an ampicillin-resistance gene fragment to visualize RescueMu. The two parental trRescueMu had been identified in the founder plant, and these size classes are marked along the right side of the autoradiogram. Hybridizing bands corresponding to new trRescueMu are indicated with a black square; the hybridizing band too small to be a full-length trRescueMu is marked with a white arrow. GP, grid G parental insertion sites 1 and 2 shown to be segregating in the progeny.