13. Your introductory lab course has set up an Ames Test experiment for you to c
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13. Your introductory lab course has set up an Ames Test experiment for you to conduct. You are given two strains to study. Strain A has a single base substitution, while Strain B has two frameshift mutations. Both strains' mutations are in genes required for synthesizing histidine. Therefore, mutant strains do not grow on media lacking this amino acid. You plate cells from each strain onto minimal media plates lacking histidine and then expose them to the indicated mutagens. Average colonies per plate Mutagen Control (no mutagen) UV (1 sec) UV (5 sec) UV (10 sec) MMS 9-aminoacridine Strain A 35 45 500 1000 350 40 Strain B -5 30 2000 2000+ 12 150 a) In this experiment, you are exposing the cells to mutagens, yet the assay counts colonies that grow, and in order to grow the cells cannot be mutant. Please explain this apparent contradiction. b) Why do you see colonies appearing on the control plates? Propose an explanation for the difference in the control frequencies observed between Strains A and B. c) A chemical is classified as a mutagen if it produces twice the number of mutants that occur spontaneously. From the data above, suggest whether UV light, MMS, and 9-aminoacridine act as effective mutagens for each strain. What do these results indicate about the types of mutations induced by each of these treatments?Explanation / Answer
Ames test is used to study the chemical, which can cause mutation. This test is used as a biological assay to test the mutagenic potential of the compound. Positive test shows chemical is mutagenic and negative test shows chemical is not mutagenic.
b) one of the alternative method used for ames test is fluctuation method. In fluctuation method, bacteria is grown with small amount of histidine added. Thus, there is gorwth of bacteria on control plate. Frequencies are different because each strain is different and its response towards mutagen is different. They respond differently for different mutagen. One has base mutation and other shows frameshift mutation.
c) from the above data, we can say that UV light acts as mutagen while the MMS and 9-aminoacridine do not show any important difference. Though they are successful in causing slight change in growth but they cannot be considered as important mutagen.
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