What that means is each one of these strands here separated. Now, when the N 15 strand is separated, the purple one, we use the N 14 isotopes. And so we basically form this molecule right over here. And likewise, when these two separate and when we use this purple N 15 band, what happens is we essentially form this molecule here. But when these two separate and instead we use the brown strand here and the brown strand here because we have the N 14 in our mixture and the N 14 will be used to synthesize that. Dodostran these are the DNA molecules that we're going to form and they're going to consist purely of these N 14 atoms.