In an experiment employing the methods of the Ames test, two his- strains of Sal

Question

In an experiment employing the methods of the Ames test, two his- strains ofSalmonella 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.

a. Characterize the expected distribution of colony growth on the four plates. Defend your growth prediction for each plate.

b. What event is being detected by growth of a colony on ay of the four plates?

Explanation / Answer

strain A = base substitution mutation = is the replacement of the one base with other

strain B = frame shif mutation = wherre they alter the reading frame of the gene code .produing non functional products .

plate 1 = control plate with strain A +s9 extract ,no EMS = no mutations but will have natural revertants {back mutations}

plate 2 = control plate with strain B +S9extract no EMS = no mutations    but will have few colonies with natural revertants , apperance of colonies is because of metabolites of s9 extract

plate 3= strain A +S9 extarct + EMS = more mutations detecting that colonies have undergone mutation because they have grown without the require ment of histidine

plate 4 Strain B +s9 extract +EMS = more mutations

salmonella species are auxotrophic mutanats , they require histidine medium to grow , inducing the mutations in the these causes the cell to grow in histidine free medium . these are construted mainly to detect frame shift mutation or point mutations in histidine producing genes . s9 extaracts are not mutagenic but there metabolic products are mutatgenic , so the number of products formed after the incubation period with the mutagens like EMS show the strains developed mutations in the genes . more is the colonies appearinf after incubation shows the strains with mutation . the main diffrence between the s9 extracts will be produced few colonies but they are natural revertants there are not mutanat.

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