Question

If Meselson and Stahl’s experiment is continued for 80 minutes (till III generation) then what would be the ratio of DNA containing N¹⁵/N¹⁵ : N¹⁵/N¹⁴ : N¹⁴/N¹⁴ in the medium?

Options

• 1 : 1 : 0

• 0 : 1 : 3

• 0 : 1 : 8

• 1 : 4 : 0

Answer 1

0 : 1 : 3

Explanation:

After three generations, the ratio is calculated as follows (assuming each generation takes 20 minutes).

Generation 0: All DNA is N¹⁵/N¹⁵.

Generation 1: All DNA is N¹⁵/N¹⁴ (hybrid).

Generation 2: Two DNA molecules, one N¹⁵/N¹⁴ and one N¹⁴/N¹⁴; 50% parental and 50% hybrid.

Generation 3: Four DNA molecules, one N¹⁵/N¹⁴ and three N¹⁴/N¹⁴; 25% parental and 75% hybrid.

Thus, the ratio of N¹⁵/N¹⁴ is 1 : 3. However, since the question asks for the ratio N¹⁵/N¹⁵ : N¹⁵/N¹⁴ : N¹⁴/N¹⁴, it would be 0 : 1 : 3.