Two groups of bacteria were cultured in different nitrogen-containing growth media. One group was grown in a medium containing the 'heavy' isotope of nitrogen, $^{15}\text{N}$, until every DNA molecule had become labelled. The other group was grown in a medium containing the 'light' isotope of nitrogen, $^{14}\text{N}$, until every DNA molecule had become labelled. The DNA from each bacterial group was extracted and then centrifuged. The diagram shows where this DNA is located in the centrifuge tubes. Bacteria with $^{15}\text{N}$ labelled DNA were moved to a medium containing $^{14}\text{N}$ and allowed to reproduce once. The DNA from the new generation of bacteria was extracted and centrifuged. Which tube shows the position of the DNA from this new generation of bacteria?
Biology 9700 · AS & A Level · Replication and division of nuclei and cells