And then we infect each one of these spots with each one of these types of lambda phages. So this lambda phage for this spot is basically infected with this lambda phage, this spot is infected with this lambda phage and so forth. And the next step, we have to go back into the lab and we synthesize a specific type of DNA probe. So we create a radioactively labeled DNA probe that has a complementary DNA sequence to that DNA fragment that we're looking for. And so what we do is we add the radioactively labeled DNA probe onto each one of these spots. And only that spot that contains that DNA fragment that we are looking for will create a hybrid with that radioactively labeled DNA molecule.