Introduce Fud genes into the fruit fly, and you get no fly: The mutated embryo dies within 10 hours. But before the unlucky Drosophila expires, an electron micrograph will show muscle lesions that look like scattered buckshot instead of the slender elegant strands of healthy muscle.

"Not many people have looked at developing muscle in a fly embryo," says Susan Abmayr, an assistant professor of molecular genetics Penn State. "We're some of the first people in the country to start identifying these kinds of genetic defects."