Question

If Meselson and Stahl’s experiment is continued for 5 generations in bacteria, the ratio of $\frac{{}_{15}N}{{}_{15}N}:\frac{{}_{15}N}{{}_{14}N}:\frac{{}_{14}N}{{}_{14}N}$ in 5th generation would be

• A. 0 : 1 : 3
• B. 0 : 1 : 7
• C. 0 : 1 : 15
• D. 0 : 1 : 31

Answer 1

The correct option is C 0 : 1 : 15

In 1st generation,
All DNA will be hybrid
Hence the ratio will be
0 Heavy : 1 Hybrid : 0 Light

In $2^{nd}$ generation,
50 % would be Hybrid$\left(\frac{{}_{15}N}{{}_{14}N}\right)$ and 50 % would be Light $\left(\frac{{}_{14}N}{{}_{14}N}\right)$
That is 0 Heavy : 1 Hybrid : 1 Light

In $3^{rd}$ generation,
25 % would be Hybrid and 75 % would be Light DNA
0 Heavy : 1 Hybrid : 3 Light)

In $4^{th}$ generation,
12.5 % would be Hybrid and 87.5 % would be Light DNA
(0 : 1 Hybrid : 7 Light)

In $5^{th}$ generation,
6.25 % would be Hybrid and 93.75 % would be Light DNA
0 Heavy : 1 Hybrid : 15 Light).