PBR322 is a plasmid having two restriction sites for EcoRI while T4 phage DNA has three restriction sites for it. These two DNA were treated with EcoRI and allowed to run on agarose gel. What kind of a pattern will be obtained on the gel?
Invalid question, T4 has around 40 sites for EcoR1, not 3...
pBR322 only has 1 site for EcoR1, between the AMP-resistance factor gene and the TET-gene...
T4 digests: (thank you, Springer Verlag!)
image taken from https://link.springer.com/article/10.1007/BF00272920
© Springer-Verlag 1981
But, if your question is more hypothetical:
both the pBR322 and the T4-genomes are circular, so:
pBR322: 2cuts = 2 fragments,
T4: 3cuts = 3 fragments.
Running on agarose gel you would see 2 bands in the pBR-lane, 3 bands in the T4-lane, UNLESS 2 or more fragments are of, or close to, equal size. . In that case they migrate more or less at the same speed and will be indistinguishable. Relative G/C to A/T ratio has an effect as well....
So in the end, if the fragments in this hypothetical example are different in size, 2 bands for pBR, 3 for T4...