The experimental proof for semiconservative replication of DNA was first shown in a

The experimental proof for semiconservative replication of DNA was first shown in a bacterium - Escherichia coli. It was discovered by Meselson and Stahl in 1958.
In this mode of replication, one strand of parent DNA is conserved in the progeny while the second is freshly synthesized. Meselson and Stahl proved the evidence for the theory by using an isotope of Nitrogen (N₁₅).