John Roger Roth (born 14 March 1939) is an American geneticist, bacterial physiologist, and evolutionist. He is a Distinguished Professor of Biological Sciences at the University of California, Davis. As instructors of the summer Advanced Bacterial Genetics course at Cold Spring Harbor Laboratory, John Roth, David Botstein, and Ron Davis taught many scientists how to use transposons and other modern molecular genetic tools for analysis of bacteria, leading to important advances in our understanding of the genetics and physiology of bacteria.