The Meselson Stahl Experiment

Introduction
Mathew meselson and Frank Stahl performed experiments to test the semi conservative method of DNA replication.
Experiment

• They grew bacteria in a medium containing Nitrogen-15 (N15), a heavy isotope of the nitrogen.
• The DNA after several generations became denser than normal because the entire bacterial DNA now contained Nitrogen-15 (N15).
• They then transferred the bacteria into a new medium containing lighter isotope Nitrogen-14 (N14) and analyzed the cultures for changes in the DNA.
• At first DNA, which the bacteria synthesized, was all heavy.
• After one round the density of the DNA fell exactly to the value one half between the all heavy isotope DNA and all light isotope DNA.

Result
This showed that after one round of replication, each of the daughter DNA duplex contained one strand of heavy isotope, after two rounds half contained none of the heavy isotope strand to form light duplex and half contained one of the heavy strand isotope.
It was now confirmed that the semi conservative method of the replication of DNA replication was true.