Tandem duplication of the fru S exon along with about 7.1 kb of 5' intronic sequence. The duplicated sequences are separated by a RS(I-CreI) flanked w[+] marker gene, in the same orientation as fru, with a FRT site at its 5' end. The 5' of the duplicated pair carries a mutation in the male-specific splice donor site of the S-exon (GTAAGC -> CTGACC).