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.[1] Branch migration is the second step of genetic recombination, following the exchange of two single strands of DNA between two homologous chromosomes.[2] 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.[1] 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.[2]