The fruit fly Drosophila melanogaster is a powerful model organism for studying animal and human development and disease. It is low cost, generates rapidly, and there are many tools to genetically modify its cells. One tool is called the Gal4/UAS two-component activation system. It is a biochemical method used to study the process of turning a gene on (gene expression) and gene function. Although it has been a mainstay of Drosophila genetics for twenty-five years, it only functions effectively in non-reproductive cells, not in egg-producing cells. It has not been known why. Now, Carnegie’s Steven DeLuca and Allan Spradling have discovered why and the have developed a new tool that can work in both cell types. The research is published in the June 2018 Genetics.