I think I get it.Thank you.which part do you not understand?0.0
Look. The DNA was at first with N15 isoptpe in it right? Now that DNA is Allowed to replicate in a medium of isotope with N14( think of them as nucleotides) Now all the DNA which had N15 would replicate ..And the free nucleotide available are of only N14 since that is the medium.
YOu remember the concetp of semi conservative replication? So the N15 DNA unwinds itself and the N14 nucloetides attach themselves to the DMA molecule adn DNA N14 and 15 combine together.And since the replication period was only ONCE so only hybrid DNA would be available.
Get it?