Assume you leave a culture inthe 37 C incubator with out tryptophan for a week instead of overnight like you planed. to your surprise the culture has shown some visible growth so you reinoculate from that flask into a new flask and see no growth in new overnight culture as expected. What kind of mutant are you dealing with?

After working with your mutant strain for a while, suddenly you run into a culture that grows normally without any supplmentation at 37C. By now you have identified the original mutation, so you resequence the entire gene and find no differrence with your earlier mutant strain. What happened?