Bacterial cells whose DNA contains only the ‘heavy’ isotope of nitrogen ($^{15}\text{N}$) are then permitted to divide for three generations in a culture medium that contains the normal isotope of nitrogen ($^{14}\text{N}$). What percentage of the DNA molecules formed have strands containing the heavy isotope of nitrogen?
- Afirst generation 50%, second generation 25%, third generation 12.5%
- Bfirst generation 75%, second generation 50%, third generation 25%
- Cfirst generation 100%, second generation 50%, third generation 25%
- Dfirst generation 100%, second generation 75%, third generation 50%