What is the Difference Between Holliday Model and Meselson-Radding Model

The key difference between Holliday Model and Meselson-Radding Model is that the Holliday model proposes the formation of a symmetric heteroduplex while the Meselson-Radding model proposes the formation of an asymmetric heteroduplex.

Recombination is a process where fragments of DNA are broken and recombined to produce genetic modifications. This process creates genetic diversity at the level of genes and reflects the differences in the DNA sequences of different organisms. Holliday Model and Meselson-Radding Model are two different models that propose critical steps of recombination.

1. Overview and Key Difference
2. What is Holliday Model
3. What is Meselson-Radding Model
4. Similarities – Holliday Model and Meselson-Radding Model
5. Holliday Model vs Meselson-Radding Model in Tabular Form
6. Summary – Holliday Model vs Meselson-Radding Model

What Holliday Model?

Holliday model is the model proposed by Robin Holliday that accounts for heteroduplex formation and gene conversion during recombination. This model proposes the critical steps of recombination, which include the pairing of homologous duplexes, formation of a heteroduplex and formation of the recombination joint, branch migration, and resolution.

Holliday Model vs Meselson-Radding Model in Tabular Form

Figure 01: Junction of Holliday Model

The process of the Holliday model formation begins with two homologous chromosomes that form the duplex DNA paired with similar sequences adjacent to each other. Next, an endonuclease cuts the corresponding region of the homologous strands of the paired duplexes. Then the cut ends dissociate from their complementary strands. Here, the arc strand invades the other duplex. Then the cut regions are sealed with DNA ligase and result in a stable joint molecule. The importance of this model is that it treats both duplexes equally. Therefore, it forms a symmetric heteroduplex.

What is Meselson-Radding Model?

Meselson-Radding Model is a model that explains gene recombination through asymmetric heteroduplex. This model conceptualizes general genetic recombination during the meiosis of newly replicated double-stranded DNA. Here, the endonuclease cuts one strand of one daughter duplex. The 5’ end dissociates and allows synthesis at the new 3′-end in order to permanently displace it. Next, the free 5’ end displaces the homologue present in the other daughter duplex. This is followed by excision of that displaced loop and ligation of the first 5′-end to the new 3′-end of the second duplex. Finally, ligation of the remaining 3′- and 5′-ends occurs through rotation to exchange the intact strands, allowing branch migration and separation.

What are the Similarities Between Holliday Model and Meselson-Radding Model?

Holliday model and Meselson-Radding model explain the recombination process.
They include endonuclease and ligase activity.
Both the Holliday model and the Meselson-Radding model comprise multiples steps.
Both form heteroduplexes during the mechanism.
They play an important role in genetic recombination and genetic diversity.

What is the Difference Between Holliday Model and Meselson-Radding Model?

Holliday model proposes the formation of a symmetric heteroduplex, while the Meselson-Radding model proposes the formation of an asymmetric heteroduplex. Thus, this is the key difference between Holliday model and Meselson-Radding model. Holliday model was proposed by Robin Holliday, while Meselson and Radding proposed the Meselson-Radding model. Moreover, the chi structure is present in the Holliday model, while it is absent in the Meselson-Radding model.

The below infographic presents the differences between Holliday model and Meselson-Radding model in tabular form for side by side comparison.

Summary – Holliday Model vs Meselson-Radding Model

Holliday model and Meselson-Radding model propose heteroduplex formation strategies during recombination. Holliday model is the model proposed by Robin Holliday that accounts for symmetric heteroduplex formation and gene conversion during recombination. Meselson-Radding model conceptualizes general genetic recombination during meiosis of newly replicated double-stranded DNA. Both models play an important role in recombination and genetic diversity. So, this summarizes the difference between Holliday Model and Meselson-Radding Model.