DNA is described as replicating by a semi-conservative mechanism. The findings from Meselson and Stahl’s experiments provided strong evidence in favour of this idea. They worked with $E.\,coli$, and its generation time is 50 minutes. The following stages took place in their experiment, but they are listed in the incorrect order. $^{14}\text{N}$ DNA refers to DNA with the ‘light’ nitrogen isotope. $^{15}\text{N}$ DNA refers to DNA with the ‘heavy’ nitrogen isotope. P All bacteria contain $^{15}\text{N}$ DNA. Q All bacteria contain hybrid DNA ($^{15}\text{N}$ DNA and $^{14}\text{N}$ DNA). R Bacteria contain either all $^{14}\text{N}$ DNA or hybrid DNA. S Bacteria grown in a $^{15}\text{N}$ medium for many generations. T Bacteria transferred to a $^{14}\text{N}$ medium and sampled every 50 minutes. Which sequence of letters gives the correct order of the stages in the experiment?
- AP S T R Q
- BP T S Q R
- CS P T Q R
- DS T P R Q