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 an FRT site at its 5' end. The 5' of the duplicated pair lacks the entire 1601bp female-specific part of the S exon.