Imagine that you have set up a genetic screen to identify E. coli mutants that cannot metabolize the amino acid tryptophan for energy. Beginning with a master plate containing many colonies, you prepare replica plates on medium with glucose or tryptophan as the only energy source. You would look for colonies that ________.
A) cannot grow on either type of media
B) can grow on both types of media
C) can grow only on the plates with tryptophan
D) can grow only on the plates with glucose

Question

Quizplus · Accepted Answer

The correct answer is D because the goal is to identify mutants that cannot metabolize tryptophan for energy. Therefore, these mutants should be able to grow on glucose (since their inability to metabolize tryptophan does not affect their ability to metabolize glucose) but not on tryptophan.

Imagine That You Have Set Up a Genetic Screen to Identify