The vertebrate Pax-6 gene product (the PAX-6 protein) triggers a complex program of gene expression resulting in formation of the vertebrate eye, which has a single lens. The fly Pax-6 gene leads to formation of the compound fly eye. When scientists cloned a mouse Pax-6 gene and introduced it into a fly embryo, it led to formation of the compound eye of a fly. What did scientists induce from this?