Holliday junction

Holliday junction, cross-shaped structure that forms during the process of genetic recombination, when two double-stranded DNA molecules become separated into four strands in order to exchange segments of genetic information. This structure is named after British geneticist Robin Holliday, who proposed the original model for homologous (or general) recombination in 1964.

Homologous recombination occurs during meiosis and is characterized by the exchange of genes between a maternal chromatid and a paternal chromatid of a homologous chromosome pair. The two parent DNA molecules, which have long stretches of similar base sequences, are separated into single strands, resulting in base pairing that leads to a four-stranded DNA structure. The Holliday junction travels along the DNA duplex by “unzipping” one strand and reforming the hydrogen bonds on the second strand.