In the summer of 1956, we learned about experiments made by Larry Morse and Esther and Joshua Lederberg on the lambda-mediated transduction (gene transfer from one bacterial strain to another by a bacteriophage serving as vector) of bacterial determinants for galactose fermentation. Since these investigators had encountered defective lysogenic strains among their transductants, we felt that such strains should be included in the collection of lambda prophage mutants under study in our laboratory. Very rapidly, thanks to the stimulating help by Jean Weigle and Grete Kellenberger, this turned out to be extremely fruitful. ... This was the end of my career as an electron microscopist and in chosing genetic and physiological approaches I became a molecular geneticist.