Chapter 8, Problem 40P

When 1 million cells of a culture of haploid yeast carrying a met^- auxotrophic mutation were plated on petri plates lacking methionine (Met), five colonies grew. You would expect cells in which the original met^- mutation was reversed (by a base change back to the original sequence) would grow on the media lacking methionine, but some of these apparent reversions could be due to a mutation in a different gene that somehow suppresses the original met^-mutations. How would you be able to determine if the mutations in your five colonies were due either to a precise reversion of the original met^-mutation or to the generation of a suppressor mutation in a gene on another chromosome?