Fig. 3. Study of transgenic lines to test the enhancer-blocking activity. (A) Transposon constructs. The maps of the constructs (not to scale) show the yellow wing (En-w) and body enhancers (En-b) as partially overlapping white boxes and the eye enhancer (Eye) as a white oval. Downward pointing arrows labeled FRT or Lox mark the target sites of the Flp or Cre recombinase, respectively. The 125 bp, 454 bp, 454^* bp, 125 bpx3 and 2 kb DNA fragments were inserted at -893 bp relative to the yellow transcription start site. The Su(Hw) insulator was inserted between yellow and white. The yellow and white genes are shown with arrows indicating the direction of transcription. (B) Analysis of yellow and white expression in males from transgenic lines heterozygous for the construct. Small symbols in the boxes indicate the number of independent transgenic lines displaying similar abdominal (black square) or eye (black circle) pigmentation. To determine the y and w phenotypes, the extent of pigmentation in the abdominal cuticle (reflecting the activity of the En-b enhancer) as well as the eye pigmentation of adult flies were estimated visually in 3- to 5-day-old males developing at 25°C (see Materials and Methods). Expression levels were determined without excision of functional elements in the wild type and after excision of the Su(Hw) insulator (Su), of the eye enhancer (E), or the tested DNA fragment (Fr). Abbreviation: su(Hw)^-, su(Hw)^v/su(Hw)^f.