DNA Cloning: The plasmid cloning vector pBR$322$ is cleaved with the restriction endonuclease Pstl$.$ An isolated DNA fragment from a eukaryotic genome $($also produced by Pstl cleavage$)$ is added to the prepared vector and ligated. The mixture of ligated DNAs is then used to transform bacteria, and plasmid$-$containing bacteria are selected by growth in the presence of tetracycline.

$($b$)$ The cloned DNA fragment is $\backslash (1,000\backslash$mathrm$\{$bp$\}\backslash )$ long and has an EcoRI site $250$ bp from one end. Three different recombinant plasmids are cleaved with EcoRI and analyzed by gel electrophoresis, giving the patterns shown below. What does each pattern say about the cloned DNA? Note that in pBR$322,$ the PstI and EcoRI restriction sites are about $750$ bp apart. The entire plasmid with no cloned insert is $\backslash (4,361\backslash$mathrm$\{$bp$\}\backslash ).$ Size markers in lane $4$ have the number of nucleotides noted.