Fig. 2. Tests of enhancer blocking by several Drosophila insulators. The structure of the yellow gene is shown. Three of the yellow enhancers are diagrammed, including the wing (white oval), body (spotted oval) and bristle (gray oval) enhancers. Insulators, illustrated as triangles (black = gypsy, white = scs, gray = scs′, diagonal hatch = Fab-7, vertical hatch = Fab-8), were inserted between the wing and body enhancers and promoter. Transposons were named according to the number and arrangement of wing and body enhancers (En) and insulators (G = gypsy, S = scs, S′ = scs′). The left column summarizes average pigmentation scores assigned for each transgene, with the total number of lines analyzed shown in parentheses. The right column summarizes the enhancer blocking status, as indicated by the pigmentation score; ‘+’ refers to an enhancer block, ‘–’ refers to no enhancer block, ‘variable’ refers to a variable enhancer blocking ability among independent transgenic lines.