What is the difference between conservative, semi-conservative, and dispersive DNA replication?

Conservative, semi-conservative, and dispersive DNA replication refer to different models of how DNA is duplicated during cell division.

Conservative replication is a theoretical model of DNA replication which suggests that the two parental DNA strands stay together after DNA replication. In this model, the original DNA molecule serves as a template for the synthesis of an entirely new molecule. The new DNA molecule consists of two newly synthesised strands, while the original DNA molecule remains intact. However, this model is not supported by experimental evidence and is not considered the primary method of DNA replication.

Semi-conservative replication, on the other hand, is the model that has been proven to be the method by which DNA replicates in cells. This model suggests that each of the two strands in the double helix acts as a template for a new strand. After replication, each new DNA molecule consists of one original (or 'parental') strand and one newly synthesised strand. This was confirmed by the famous Meselson-Stahl experiment in 1958, which used isotopes of nitrogen to trace the replication process.

Dispersive replication is another theoretical model which proposes that both parental strands are dispersed into two new double helices following replication. In this model, each strand of both daughter molecules contains a mixture of old and newly synthesised DNA. This model, like the conservative model, is not supported by experimental evidence.

IB Biology Tutor Summary: DNA replication occurs when cells divide, with three models proposed for how it happens. Conservative replication theorises that original DNA remains intact, forming a new molecule entirely. Semi-conservative replication, proven by experiments, involves each DNA strand making a new counterpart. Dispersive replication suggests DNA mixes in new molecules. Only semi-conservative replication is experimentally validated.