HollidaySegarFormel

The Holliday-Segregation model, often referred to as the Holliday-Segar model or Holliday model, is a theoretical framework in molecular biology that explains the process of homologous recombination during DNA repair and genetic diversity. Proposed independently by Robin Holliday in 1964 and later refined by other researchers, including those associated with the name "Segar," it describes how genetic material is exchanged between two homologous DNA molecules, leading to crossover events.

The model begins with the formation of a double-strand break (DSB) in one of the DNA molecules. The broken strand invades the intact homologous DNA, forming a displacement loop (D-loop) where base pairing occurs between the complementary strands. This creates a structure known as a Holliday junction, a four-way crossroads where the strands from each molecule are intertwined. The Holliday junction can migrate along the DNA, allowing for further exchange of genetic material between the two strands.

The resolution of the Holliday junction determines whether a crossover or a non-crossover outcome occurs. If the junction is resolved by cutting across the strands (heteroduplex resolution), a crossover event takes place, resulting in the exchange of genetic material between the two DNA molecules. If the junction is resolved by cutting along the strands (non-crossover resolution), the original DNA molecules are restored, preserving genetic continuity without crossover.

This model is fundamental in understanding mechanisms of DNA repair, particularly in the context of non-homologous end joining (NHEJ) and homologous recombination repair (HRR). It also plays a role in explaining genetic recombination during meiosis, contributing to genetic diversity in sexually reproducing organisms. The Holliday-Segar model remains a cornerstone in the study of DNA metabolism and genetic stability.