Bacteria were grown for many generations in a medium containing a heavy isotope of nitrogen, ${}^{15}N$. They were then transferred to a medium containing the light isotope of nitrogen, ${}^{14}N$. They were given time to replicate DNA and divide once. Their DNA was extracted, spun in a centrifuge and observed using ultra violet light. The DNA with the ${}^{15}N$ settled at a lower depth than the DNA with the ${}^{14}N$.
Which shows the predicted results after one generation in the medium with the light isotope?
1 )
A
2 )
B
C
4 )
D
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