DNA is said to replicate in a semi-conservative way.
Results of Meselson and Stahl’s experiments gave overwhelming support to this theory. They used E. coli which has a generation time of 50 minutes.
Here are the stages occuring in their experiment but they are in the wrong order. ${}^{14}N$ DNA contains the ‘light’ isotope of nitrogen. ${}^{15}N$ DNA contains the ‘heavy’ isotope.
P All bacteria contain 15N DNA.
Q All bacteria contain hybrid DNA (${}^{15}N$ DNA and ${}^{14}N$ DNA).
R Bacteria contain either all ${}^{14}N$ DNA or hybrid DNA.
S Bacteria grown in a ${}^{15}N$ medium for many generations.
T Bacteria transferred to a ${}^{14}N$ medium and sampled every 50 minutes.
Which sequence of letters shows the correct order of the stages in the experiment?
1 )
$P \to S \to T \to R \to Q$
2 )
$P \to T \to S \to Q \to R$
$S \to P \to T \to Q \to R$
4 )
$S \to T \to P \to R \to Q$
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