BAC clone CH321-18I14, that encompasses sna and Tim17b2, mutated so that the primary sna enhancer (containing a cluster of dl and twi protein binding sites) in the immediate 5' flanking region of the sna transcription unit has been replaced by random DNA. A second cluster of dl and twi protein binding sites located within the neighbouring Tim17b2 locus (the 'shadow enhancer') is still present.