Transposon hopping from the 7M donor locus. (a) The outcross progeny from nine 7M hopper adults were scored for changes in GFP intensity indicative of transposon remobilization. The 7M donor locus contains a concatemer of approximately eight to ten pT2 βGFP transposons on chromosome 10. The remobilization frequency is expressed as a percentage of GFP bright tadpoles observed in the GFP-positive outcross population. 7M hopper frogs 7M♂9 and 7M♂11 are 'functionally homozygous' for both the transposon substrate allele and the transposase enzyme transgene (see text for details), and display higher remobilization activity (approximately 1.8%) than their 'heterozygous' male hopper littermates (7M♂1, 7M♂2, 7M♂3, 7M♂5, 7M♂14, 7M♂20; approximately 0.44%). Outcross of 7M hopper 7M♀25 produced a remobilization rate of > 4%. (b) Schematic representation of the X. tropicalis chromosomes indicating the distribution of remobilized SB transposons. The parental 7M donor site (thick line) is located on scaffold 38 which maps to chromosome 10. Remobilization of discrete transposons away from the 7M donor locus is represented by the grey arrows. (Not to scale.) (c) Fluorescence in situ hybridization of metaphase chromosomes verifies that the 7M parental donor locus is located near a telomere of X. tropicalis chromosome 10. GFP: green fluorescence protein; SB: Sleeping Beauty.