An E.coli cell containing hybrid DNA was placed in a medium containing heavy nitrogen (¹⁵N). Calculate the percentage of heavy, light and hybrid DNA after 2 generations in the same medium (¹⁵N).

Initially DNA contain ¹⁵N¹⁴N

Then it is placed in a medium containing ¹⁵N for 2 generation.

After 1 generation:

¹⁵N¹⁴N→ ¹⁵N¹⁴N    ¹⁵N¹⁵N

After 2^nd generation

¹⁵N¹⁴N    ¹⁵N¹⁵N→ ¹⁵N¹⁴N    ¹⁵N¹⁵N   ¹⁵N¹⁵N    ¹⁵N¹⁵N

Therefore, we can clearly see that 75% of DNA formed is heavy and 25% of the DNA is hybrid.