To isolate DNA at a molecular level, first we must use restriction enzymes to cut the DNA into fragments. After this we run the framents through gel electrophoresis where they are separated on the basis of size.
To identify the gene of interest we first make a probe complimentary to the gene of interest. Transfer the fragments onto a nitrocellulose membrane and then identify the gene with the help of the probe. This is known as Southern blotting.
Finally the gene of interest is cut out from the gel, also known as elution.