Question

If Meselson and Stahl's experiment is continued for four generations in bacteria, the ratio of $^{15}N/^{15}N : ^{15}N/^{14}N :^{ 14}N/^{14}N$ containing $DNA$ in the fourth generation would be

• A. $1 :1 :0$
• B. $1 : 4 : 0$
• C. $0 : 1 : 3$
• D. $0 : 1 : 7$

Answer 1

Answer: (D)

$0 : 1 : 7$

Answer 2

As per Meselson and Stahl's experiment, parent $DNA$ was first isolated from E.coli grown in heavy $^{15}N$ medium. It was then put in light $^{14}N$ medium. $DNA$ shows semi conservative nature, hence, in fourth generation, the ratio of $^{15}N/^{15}N : ^{15}N/^{14}N : ^{14}N/^{14}N$ will be $0 :1 : 7$.