7kb SalI-HindIII genomic fragment containing ovo, with a stop codon introduced at position 3960 (60 residues after the beginning of exon 2b). In addition, the ovo open reading frame is tagged at the C-terminal end (two codons upstream of the stop codon) with lacZ. The presence of the stop codon in exon 2b means that only mRNAs that have spliced out this exon give rise to a ovo ::lacZ fusion protein.