Question

If E. coli was allowed to grow for 80 minutes then what would be the proportions of light and hybrid densities DNA molecule?

Answer 1

E. coli divides in 20 minutes. So, after 80 minutes there will be 4 generations. In the first generation all the strands will be hybrid (as the heavy isotope will be incorporated in the newly synthesised strand of DNA) i.e the two DNA will be of intermediate nature. In the second generation, 50% the DNA will be light and 50% will be hybrid. In the 3rd generation, 25% will be hybrid and 75% will be light and in the fourth generation 12.5% will be hybrid and 87.5% will be light strand.