question_answer 36)

  If Meselson and Stahl's experiment is continued for four generations in bacteria, the ratio of /:/:/, containing DNAin the fourth generation would be (a) 1:1:0                (b) 1:4:0               (c) 0:1:3                (d) 0:1:7

Answer:

                  (d)Meselson and Stahl found that DNA of the first generation was hybrid or intermediate (and). It settled in caesium chloride at a level higher than the fully labeled DNA of parent bacteria (). The second generation of bacteria after 40 minutes, contained two types of DNA, 50% light() and 50% intermediate(). The third generation of bacteria after 60minutes contained two types of DNA, 25%intermediate (N15 N14) and 75% light (N14 N14) in 1:3 ratio. The fourth generation after80 minutes contained 12.5%N15 N14 and 87.5% N14N14 DNA in 1:7 ratio.