In an experiment, bacteria were grown for 500 generations in a medium containing ¹⁴ N (light isotope), then transferred to a medium with ¹⁵ N (heavy isotope) for one generation, and finally transferred back to the ¹⁴ N medium for one more generation. Assuming all cells divide synchronously and replication is semi-conservative, the ratio of ¹⁴ N ¹⁵ N to ¹⁴ N ¹⁴ N double-stranded DNA at the end of the experiment is:

Step-by-step solution

Initially, bacteria are grown in ¹⁴ N medium for 500 generations, so all DNA molecules are ¹⁴ N ¹⁴ N (light). Let the initial number of DNA molecules be x . Upon transfer to ¹⁵ N medium for one generation, the DNA replicates semi-conservatively. The two ¹⁴ N strands of each molecule separate and act as templates to synthesize new ¹⁵ N strands. This results in 2x molecules of ¹⁴ N ¹⁵ N (hybrid) DNA. Upon transfer back to ¹⁴ N medium for one more generation, the 2x hybrid molecules separate into 2x strands of ¹⁴ N an