If you insert a -galactosidase gene lacking its own transcription control region into a cluster of piRNA

If you insert a β-galactosidase gene lacking its own transcription control region into a cluster of piRNA genes in Drosophila, you find that β-galactosidase expression from a normal copy elsewhere in the genome is strongly inhibited in the fly’s germ cells. If the inactive β-galactosidase gene is inserted outside the piRNA gene cluster, the normal gene is properly expressed. What do you suppose is the basis for this observation? How would you test your hypothesis?