What model of DNA replication was established by Meselson and Stahl?

The semi-conservative model of DNA replication established by Meselson and Stahl is based on the concept that during DNA replication, each of the two strands of the original DNA molecule serves as a template for the formation of new complementary strands. This means that when a DNA molecule replicates, the two new double helices each consist of one original strand and one newly synthesized strand.

Meselson and Stahl conducted a series of experiments using isotopes of nitrogen to label DNA and demonstrated that after one round of replication, the density of the DNA molecule indicated that it was composed of one parental strand and one newly formed strand, supporting the semi-conservative hypothesis. This was shown by the appearance of hybrid DNA molecules after replication, which had intermediate density compared to the fully labeled parental DNA and the fully unlabeled new strand.

This finding was significant because it contradicted the conservative model, where one would expect the parental strands to remain together and completely new strands to be formed; and the dispersive model, where the parental DNA would be mixed throughout the new strands. The semi-conservative model was ultimately confirmed as the mechanism of DNA replication used by cells, firmly establishing its role in genetic inheritance.