The Act5C promoter is fused upstream of sequence encoding an N-terminal myristoylation signal (Tag:Myr(Src64B)) and a mCherry coding sequence. The reading frame of both coding sequences has been interrupted. The Tag:Myr(Src64B) reading frame is interrupted by a CaSSA switch cassette that contains the target site to the 'gRNA#2' guide RNA flanked on each side by a direct repeat of part of the Tag:Myr(Src64B) sequence. The mCherry reading frame is interrupted by a CaSSA switch cassette that contains the target site to the 'gRNA#1' guide RNA flanked on each side by a 400bp direct repeat of part of the mCherry sequence. Designed as part of a CaSSA system: if a double-strand break is induced using Cas9 and the appropriate guide RNAs, strand annealing (SSA) repair can reconstitute a functional Tag:Myr(Src64B)-tagged mCherry reporter that is expressed in the cell in which the repair occurs and also in any of its progeny. For this transgene, both the 'gRNA#1' and 'gRNA#2' guide RNAs must be provided to reconstitute the functional reporter, as SSA of both CaSSA switch cassettes must occur to reconstitute a single open reading frame.