Transgenic construct used to study the requirements for amplification of the third chromosome chorion gene cluster. Contains (5' to 3'): a gypsy insulator - a 2.4kb genomic fragment from the chorion gene cluster (this includes the ACE3 amplification control element, the Cp18 transcription unit and the Ori-β origin of replication) - the y+mDint2 marker - a gypsy insulator.