And that's because the initial equalize cells that we took out from this beaker consisted of these radioactively labeled DNA molecules. So before replication occurred, all cells had heavy DNA and this was represented by a single band along the following diagram. Now, following one replication, when we extract the DNA from the first generation cells that came from those initial equalized cells, this is the band that we found. And notice we also had a single band just like in this case. But this band was shifted to the left along this diagram, along the photograph. And what this basically means is we have a single type of DNA molecule because we have that single band but it is lighter, less dense than in this particular case because it is found farther to the left along the x axis.