Q. 22. If Meselson and Stahl's experiment is continued for four generations in bacteria, the ratio of 15N/ 15N:15N/14N:14N/14N containing DNA in the fourth generation would be:
(a) 1 : 1 : 0
(b) 1 : 4 : 0
(c) 0 : 1 : 3
(d) 0 : 1 : 7
(d) Meselson and Stahl found that DNA of the first generation was hybrid or intermediate (N15 and N14). It settled in caesium chloride at a level higher than the fully labelled DNA of parent bacteria (N14 N14) in 1 : 3 ratio. The fourth generation after 80 minutes contained 12.5% N15 N14 and 87.5% N14 N14 DNA in 1 : 7 ratio.
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