Scientists used their understanding of the MAT (mating) genes to induce penicillin mold to reproduce sexually, producing spores with new gene combinations. They hope to breed new strains that will kill antibiotic-resistant disease germs. And now that they have induced penicillin to breed, instead of merely producing identical spores, for the first time in a hundred years, they’ll try the same with other important fungi, such as those that produce other antibiotics.