Index >> Replication of DNA >> Semi Conservative Replication Process

Semi Conservative Replication Process - Watson and Crick were aware that any model of DNA structure should be able to explain replication. Delbruck suggested that the Watson Crick model of DNA could theoretically replicate by three modes, conservative, semiconservative and dispersive.

(1) According to the conservative mode, of the two double helices formed one would be entirely of old material and the other entirely of new material. Thus the old parent double helix would be unchanged.

(2) According to the semi Conservative mode proposed by Watson and Crick, each strand of the two double helices formed would have one old and one new strand.

If DNA replicated conservatively one would expect to find two layers, one of N14 and the other of N15, in the first generation, and similarly for subsequent generations .With dispersive replication, tubes of all generations would be expected to show a single layer (N14+N15), since the DNA would contain both new and old materialmixed up.

In semi conservative replication the first generation would be expected to show a hybrid N1.+NI5 layer. With each generation after the second the N14 layer would show a greater accumulation of material. Actual observations correspond to this expectation. This shows that replication of DNA is of the semi conservative manner proposed by Watson and Crick. i.e. that the double strands formed are identical to the parent strand.