How are the cleaved DNA fragments from two sources able to recombine?
Cleaved DNA fragments from 2 sources can only recombine artificially. This does not occur naturally. Recombination is accomplished by chemically altering one strand, resulting in the removal of a sequence of bases, then altering a second DNA strand from another source with the same base sequence as the first strand, so the second strand's bases align with the first. This creates a new molecule. See link below for a graphic: