The answer is C.
The key says that they knew it was BamHI because lane 2 is absent in the blot, so we know it cut gene X.
From my understanding, after the blot, probes are introduced to the solution.
Anything that the probe does not bind does not show up on the blot. Anything that the probe does bind to, does show up on the blot. (ie. lane 1 and 3)
I think I am just not understanding how they came to the conclusion that since lane 2 did not show up on the blot, we know that they cut through gene x.
Is it because the probe needs to complementarily bind to the whole gene x and not a chopped up one, and that's why we can deduce the gene was cut in some way?
Please correct me if I am wrong, as I am pretty weak in microbio techniques.