What is 'semi- conservative' DNA replication ? How was it experimentally proved and by whom ?

Explanation

The two strands of DNA separate and act as a template for the synthesis of new comlementary strands . After the completion of replication, each DNA molecule has one parental and one newly sytnthesized strands and this schems was termed a semiconservative DNA replication .
DNA replication is auto catalytic , it occurs during S-phase of cell cyele . Watson and Crick Proposed semi conservative mode of replication for DNA. 1985 Meselson and Stahl's proved the semi- conservative mode of replication. They worked with E. coli using a heavy isotope of Nitrogen, `N^(15) , E.` coli was grown with `N^(15)` for several generation till the bacteria become completely labelled with `N^(15)` . They were then shifted to medium with normal `N^(14)` nitrogen. Samples were taken after every generation and tested for the presence of `N^(15) and N^(14)` using density gradient centrifugation with CsCI. The first generation was found to be hybrid between `N^(15) and N^(14)` second generation contain two types of DNA, 50%, light `(N^(14))` and 50% intermediate. This is only possible if two strands separate during repllication and act as a template for synthesis of new Complementary strands, thus proving a semiconservative mode of replication.