Question

After 60 min, in Meselson and Stahl experiment, what percentage of DNA would be light, hybrid and heavy respectively?

• A. 0, 100, 0
• B. 50, 50, 0
• C. 0, 0, 100
• D. 75, 25, 0

Answer 1

The correct option is D 75, 25, 0

E. coli takes 20 minutes to replicate its genome. Therefore,
0 min: 1 Heavy Helix (100% heavy)
$\downarrow$
20 min: 2 Hybrid Helix (100% hybrid)
$\downarrow$
40 min: 2 Hybrid +2 light Helix (50% hybrid, 50% light)
$\downarrow$
60 min: 2 Hybrid +6 light Helix (25% hybrid and 75% light in 1:3 ratio)