Characterize the expected distribution of colony growth on the four plates. The
ID: 201630 • Letter: C
Question
Characterize the expected distribution of colony growth on the four plates.
The Ames test identifies mutagenic chemical compounds by testing for increased reversion rates in auxotrophic bacteria exposed to a test compound in the pres liver In an experiment employing the methods of the Ames test, two his strains of Salmonella are used. Strain A contains a base substitution mutation, and Strain B contains a frameshift mutation. Four plates are prepared to test the mutagenicity of the compound ethyl methanesulfonate (EMS). Plate 1 is a control plate with Strain A and S9 extract but no EMS. Plate 2 is also a control plate and contains Strain B and S9 extract but no EMS. Plate 3 contains Strain A along with S9 extract and EMS, and Plate 4 contains Strain B, S9 extract, and EMS ence of detoxifying enzymes from the eukaryoticExplanation / Answer
Plate I = Strain A + S9 extract
Plate II = Strain B + S9 extract
Plate III = Strain A + S9 extract + EMS
Plate IV = Strain B + S9 extract + EMS
Plates I and II are control plates. They will have the relatively low number of colonies on the selection plate. They represent background SPONTANEOUS REVERSIONS.
Plate III may have more colonies than plates I, II, and IV because the INDUCED REVERSION rate would likely be higher for plate III that plates I, II, and IV.
Plate III will have significantly more colonies than plate I because EMS is a known mutagen that causes base-pair substitutions.