Three theories existed:
- The parent DNA molecule breaks into segments and new nucleotides fill in the gaps precisely (fragmentation theory).
- The complete parent DNA molecule acts as a template for the new daughter molecule, which is assembled from new nucleotides. The parent molecule is unchanged (conservative hypothesis).
- The parent DNA molecule separates into its two component strands, each of which acts as a template for the formation of a new complementary strand. The two daughter molecules therefore contain half the parent DNA and half new DNA (semi-conservative hypothesis).
The semi conservative hypothesis was shown to be the true mechanism by the work of Meselsohn and Stahl(1958).
In their experiment they grew the bacterium E.coli in the presence of radioactive 15N until a culture was obtained in which all the DNA was labelled with …