NEET 2022 Botany Messelson & Stahl Experiment MCQ Question

Chapter: Molecular Basis of Inheritance

Class: 12 Topic: Meselson & Stahl Experiment Difficulty: 🔴 Hard

✅ Ans: A — 60 cells

E. coli generation time = 20 min.

After 60 min:

$$60/20=3\text{ generations}$$

Starting with 10 cells:

$$10\times2^3=80\text{ cells}$$

After 3 generations of semiconservative replication, $\frac34$ of the DNA molecules are completely $^{14}N$.

$$80\times\frac34=60$$

🧠 NEET Trick

After $n$ generations: total cells = $N_0 2^n$. After the first generation, only hybrid DNA exists; subsequently the fraction of completely light DNA increases.

Answer: 60 cells