Q. E.coli cells having DNA radio labelled with $^{15}N$ were placed in culture medium containing non radioactive $N^{14}$ isotope for three generations. What will be the percentage of ratioactivity in DNA of the progeny?
UP CPMTUP CPMT 2014
Solution:
At start, both the strands of DNA will have radioactive isotope and thus radioactivity is $100\%$. In next generation, after semi-conservative replication of DNA, $50\%$ radioactivity is found which is halved with each subsequent replication. Thus, after three generations, $12.5\%$ radioactivity will be found in bacterial culture.
