- #1

mastiffcacher

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## Homework Statement

I have to calculate the mutant frequency from a bacterial culture. We were looking at mutations in the

*lac*operon due to the ability to easily see when the mutation occurred. A lac- culture was plated on lacXMM and TSA. The number of revertants on the lacXMM was calculated to be 2.6x10^4 and the number of colonies was 2.26x10^9 on the TSA. These numbers were calculated after an overnight incubation period.

## Homework Equations

2^x=N where N is the number of cells and x is the number of cell divisions

mutant frequency= # mutants/# of cell divisions

## The Attempt at a Solution

Here is my problem. When I use the formulas given to me, I get the # of cell divisions to be 31.07 and a mutant frequency of 836.7. I am not quite sure what this number means. Last week, we were told that we could just use the # of CFU on lacXMM/ # of CFU on TSA. We were told that this was acceptable due to the number of cell divisions being high and that this somehow equaled out. I am not sure what was meant. When I simply do it this way, I get 1.1x10^-5 which I assume means that there are 1.1x10^-5 mutations per cell division.

So which way is correct and why exactly? The second answer is more in line with what I would think that the correct answer is but then why is the other formula the one that I find when I try and look it up? Any insight would be appreciated.