Transgenic construct used in a study of the Fab-7 element. Contains two divergently transcribed reporters: a w+C marker and a lacZ reporter driven by a minimal eve promoter. A 200bp SpeI-BamHI enhancer fragment that directs expression of the h stripe 1 (H1), a 1kb spacer (MAR region of the mouse μ light chain gene) and a 1kb SalI IAB5 enhancer fragment from the iab-5 cis regulatory region of Abd-B have been inserted between the two divergent promoters.