Bacteria were cultured in a medium that contained $^{15}\text{N}$. After several generations, all of them contained $^{15}\text{N}$. A number of these bacteria were then moved to a medium containing the nitrogen isotope $^{14}\text{N}$. The bacteria were allowed to divide once. DNA from some of the bacteria was extracted and analysed. This DNA was entirely hybrid DNA, with equal amounts of $^{14}\text{N}$ and $^{15}\text{N}$. Some bacteria from the medium with $^{15}\text{N}$ were transferred to a medium of $^{14}\text{N}$. They were allowed to divide twice. The graph shows the percentages of $^{14}\text{N}$ and $^{15}\text{N}$ in the DNA of these bacteria. Some bacteria from the medium with $^{15}\text{N}$ were transferred to a medium of $^{14}\text{N}$. They were allowed to divide three times. What would be the percentages of $^{14}\text{N}$ and $^{15}\text{N}$ in the DNA extracted from these bacteria?
Biology 9700 · AS & A Level · Replication and division of nuclei and cells