Question

If Meselon and Stahl's experiment is continued for four generations in bacteria, the ratio of N${}^{15}$N${}^{15}$, N${}^{15}$N${}^{14}$, N${}^{14}$N${}^{14}$ 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

The correct option is D $0:1:7$

Meselson and Stahl's experiment is based on the semi-conservative replication of the DNA. It means that when a parental DNA undergoes replication, each strand of the parental DNA serves as a template and the new daughter strand is synthesized on the template strand. Keeping the semi-conservative replication in view, and starting with DNA strands having N${}^{1}5$ and thereafter N${}^{1}4$, the number of heavy, hybrid, and light chains are as follows-

In the fourth generation, n = 4,

The number of heavy chains is zero and the number of light chains are always two.

By using $2^n-2$, we can find out the light chains.

Thus, there are total 14 light chains, i.e., N${}^{15}$N${}^{14}$. Therefore, N${}^{15}$N${}^{15}$ is 0 , N${}^{15}$N${}^{14}$ is 2, N${}^{14}$N${}^{14}$ is 14.

So, the correct answer is option D.

14