What is the name of the four-way DNA junction formed during recombination?

The four-way DNA junction formed during recombination is called a Holliday junction.

It is a branched structure in which four double-stranded DNA arms meet. During homologous recombination, strands from two similar DNA molecules exchange partners, creating a crossover point. The junction can move along the DNA through branch migration, allowing more genetic material to be exchanged.

The structure is named after British molecular biologist Robin Holliday, who proposed the model in 1964 while explaining gene conversion in fungi. Holliday junctions are also important in repairing DNA double-strand breaks. Enzymes called resolvases eventually cut or process the junction so the recombined DNA molecules can separate.

A common mix-up is the replication fork, which is a Y-shaped structure where DNA is copied; it is not the four-armed crossover structure produced by recombination. Holliday junctions have also become useful in DNA nanotechnology, where engineered versions act as molecular building blocks.