Bacteria were cultivated in a medium in which heavy nitrogen, $^{15}\text{N}$, was the only nitrogen source. After many generations, every bacterial DNA molecule contained heavy nitrogen. The bacteria were then transferred from the heavy nitrogen medium to a medium containing only light nitrogen, $^{14}\text{N}$. Bacteria were taken from each of the following three generations and their DNA was examined. Hybrid DNA includes both heavy and light nitrogen. Which row gives the correct DNA for the first and third generations?
- Afirst generation: all hybrid; third generation: half hybrid, half light
- Bfirst generation: all hybrid; third generation: one quarter hybrid, three quarters light
- Cfirst generation: half hybrid, half heavy; third generation: half hybrid, one quarter heavy, one quarter light
- Dfirst generation: half hybrid, half light; third generation: one quarter hybrid, three quarters light