For example, we use radioactively heavy phosphorus atoms. And what that will allow us to do is in step four, we're going to be able to use x ray autorediography to basically find exactly where that DNA molecule is. So in step three, a specific restriction fragment of interest. So this seed can be detected by creating and adding a radioactively labeled complementary DNA strand to that polymer sheet. Since it is complementary to the gene of interest, it will hybridize with the fragment of interest. So it will basically form a double stranded, form a double stranded helix.