And so these two individual single strands exist as single strands. Now, when we add that DNA probe that has been radioactively labeled by, let's say, a heavy phosphorous atom, so what will happen is, because the sequence is complementary to this sequence here, the green radioactively labeled DNA probe will hybridize, will form a double helix structure with that single stranded complementary molecule. And so now this has been radioactively labeled. And notice this DNA probe will not form the same double helix with any of these other bands because the other bands don't have that complementary sequence. So this molecule is a single stranded DNA fragment of interest that we want to actually detect. And the green molecule is that radioactively labeled DNA probe that contains a nucleotide sequence that is complementary to that restriction fragment above that we essentially want to detect.