Branch migration
![Diagram illustrating the movement of a branch point between two homologous pieces of DNA. Migration travels to the left and stops when it reaches the end of the homologous region. The second branch point on the right is free to move in either direction as well.](/Images/godic/202501/01/page1-261px-Branch_migration_1.pdf5236.jpg")
![Open X structure of a Holliday junction. RuvA binds to the DNA and fits in between the double strands on all four sides. RuvA also has a domain that fits inside the centre of the junction.](/Images/godic/202501/01/Holliday_junction_coloured5236.png")
![The Holliday junction converts between the open X structure (top) and the stacked X structure (bottom) depending on the Mg2+ concentration.](/Images/godic/202501/01/Holliday_junction_stacking_isomers.svg5237.png")
Branch migration is the process by which base pairs on homologous DNA strands are consecutively exchanged at a Holliday junction, moving the branch point up or down the DNA sequence. Branch migration is the second step of genetic recombination, following the exchange of two single strands of DNA between two homologous chromosomes. The process is random, and the branch point can be displaced in either direction on the strand, influencing the degree of which the genetic material is exchanged. Branch migration can also be seen in DNA repair and replication, when filling in gaps in the sequence. It can also be seen when a foreign piece of DNA invades the strand.