Bruce ames constructed a mutagenicity test which initially missed carcinogens which were noncarcinogenic to the tester strains. why?
a. tester strains were more resistant to the mutagenic effects of the carcinogen than eukaryotes
b. not all carcinogens are mutagens
c. potential carcinogens needed to be modified in eukaryotes before they were mutagenic
d. histidine biosynthesis was inhibited by the presence of the carcinogens
e. the organism used in the test is a pathogen of mice

C: Potential carcinogens needed to be modified in eukaryotes before they were mutagenic

Explanation:

Previous carcinogenic tests used live animals and costly and time-consuming processes. This rendered animal testing unworkable for use in broad scale screening and lowered the amount of compounds that could be tested.

Ames test utilizes the Salmonella typhimurium bacteria to test for mutagens and is much cheaper and quicker. Since Salmonella is a prokaryote the way bacteria react is different from eukaryotes because they have slightly different mechanisms in the way DNA replicates.