One of them is the normal deoxy adenosine triphosphate. The other one is a dioxy adenosine triphosphate. And the dioxia adenosine triphosphate does not contain a hydroxyl group on the third prime carbon. And what that means is if that DNA polymerase actually uses the Ddatp to place this base, it will not be able to continue that DNA replication process because that molecule does not have the hydroxyl group that is needed to produce the phosphor diester bond with the next base. And so if this A comes from the Ddatp, this process will end and this will be the molecule that we will synthesize. And this is why we have fragment number one, molecule number one.