I'm a little confused as to how to figure out the formula needed to figure this out.

I have a plasmid that is 7.3Kb and am told that it is cut with an enzyme of 4bp. For some reason I thought that the formula needed to figure this out is:

(1/4)^4 x 7300

But it gives me such a low number that I don't think it's right so I'm just a little confused.

  • $\begingroup$ Do not work from formulae people give you. Work from logic. You will find it here, among other places. $\endgroup$ – David Nov 19 '17 at 15:07

There are $4^4$ 4-cutters, which means that given a 4 cutter, you expect it to cut once every 256 bases on average. $7300/256 = 28.5$, so you expect 28 or 29 cut sites in the plasmid. This is identical to what you calculated.


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