After two generations of replication in the Meselson and Stahlexperiment, what was the composition of the two bands?One band was all 14N and one band was half 14N and half 15N.One band was all 15N and one band was half 14N and half 15N.One band was all 14N and one band was all 15N.One band was all 15N and one band was one quarter 14N and threequarters 15N.One band was all 14N and one band was one quarter 14N and threequarters 15N.

Meselson and Stahl conducted their experiment of DNA replication on E.coli bacteria using heavy isotope of nitrogen and came into final conclusion that DNA replicated semi- conservatively. That is each strand in DNA molecule serves as templated for synthesis of new complementary strands. They grew bacteria for many generation containing primarily of heavy nitrogen isotopes and then examined with analytical centrifuge and found that DNA isolated from this produces single heavy band. Then they transferred some portion of culture to new medium which now consists of light nitrogen isotope instead of previously heavy one. When DNA was isolated from these after one generation they found out that single band was lighter than one obtained before, and the heavy band could not be observed as it was earlier. When DNA is isolated from the same culture after two generations, they observed two distinct bands of equal intensity, one with same weight as previous one and other new one was lighter. When DNA from the same culture after three generation, this lightest band became the predominant one and the band in the middle just faded. So, as per the experiment conducted by Meselson and Stahl, it can be concluded that after two generations in light medium, the heavy and light strands separate and both replace with light nitrogen. Half therefore become light/light and half becomes heavy/light. Hence, answer is option A