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Meselson-Stahl experimental results

After the first replication, each DNA molecule contained 50% $$\ce{^{15}N}$$ and 50% $$\ce{^1^4N}$$. All the DNA molecules were $$\ce{^1^4N}$$/$$\ce{^1^5N}$$ hybrids.

This excluded the conservative hypothesis. If it had been correct, half of the DNA molecules would contain only $$\ce{^{15}N}$$ and the other would contain only $$\ce{^{14}N}$$.

After the second replication, half the strands were made up of 50% $$\ce{^1^5N}$$ and 50% $$\ce{^1^4N}$$ and the other half entirely $$\ce{^1^4N}$$.

Dispersive replication would have predicted that all DNA consists of 25% $$\ce{^{15}N}$$ and 75% $$\ce{^{14}N}$$ but this was not the case.

The experiment lent support to semi-conservative replication.

Percentage of DNA
Generation Purely $$\ce{^1^4N}$$ $$\ce{^1^4N}$$/$$\ce{^1^5N}$$ hybrid Purely $$\ce{^1^5N}$$
0 0% 0% 100%
1 0% 100% 0%
2 50% 50% 0%