The replication of DNA in Escherichia coli.

The so-called Meselson-Stahl experiment, the first proof of semi-conservative replication of DNA. Semi-conservative replication describes the mechanism of DNA replication in all known cells. It derives its name from the production of two copies of the original DNA molecule, each of which contains one original strand, and one newly-synthesized strand. Digital facsimile from pnas.org at this link.